The first days of spring are the perfect time to kick back, relax and get ready for a new MLB season and all the possibilities it might bring. We’ve previewed all six divisions already at FiveThirtyEight, but we still had some deep thoughts about baseball’s Big Questions. That’s why we’ve prepared a guidebook of sorts for what to watch for in 2017, with an eye on where the game is headed. Here are 10 topics we’ll be thinking — and writing — about throughout the season:

Did the Cubs prove tanking works?

In many ways, the 2016 Chicago Cubs were an inimitable team. They started with one of the most hyped rosters in MLB history, somehow surpassed even those lofty expectations for most of the regular season, then survived a treacherous postseason to win the World Series and finally set down a burden they’d carried for 108 years. For better and for worse, that’s not a path most franchises are in a position to take.

But it won’t stop other clubs from trying to replicate elements of the Cubs’ success. And one major area where they might try to borrow from Chicago’s blueprint is in the reinvigorated notion of the “success cycle.” Longtime friend-of-FiveThirtyEight Jonah Keri introduced the concept in the early 2000s as a way to formalize the idea that teams undergo a cycle of rising and falling, building and tearing down rosters at regular intervals. Keri later disavowed the idea, but it might be on the way back after the Cubs’ rebuilding (or, as the less charitable among us might call it, “tanking”) effort under GM Theo Epstein bore such delicious fruit the past few seasons.

At the same time that Epstein was executing his rebuild in Chicago, the Houston Astros were doing something similar (to good effect, with even more success potentially on the way), and the Brewers, Braves and Phillies are currently letting their fields lie fallow. League-wide, just two key characteristics — a team’s payroll and its average age — explained a whopping 58 percent of the variation in win-loss records during the 2016 season, the highest that mark has been since at least 1998. Both of those characteristics are strongly associated with how a team tries to manipulate where it is in the success cycle

It’s hard to blame Keri for writing off the success cycle; when he was re-evaluating it after the 2010 season, age and payroll had just gotten done explaining a mere 14 percent of the variation in records. In other words, as recently as a few years ago, the familiar patterns of team-building seemed to have been broken. But in an odd twist, maybe the relevance of the success cycle follows its own cyclical pattern. If that’s the case, the Cubs capitalized on it at exactly the right time. –Neil

Will the shift keep getting more popular?

Baseball’s swift adoption of the defensive shift stands as one of sabermetrics’ shining achievements, turning what was a seldom-used tactic in the early 2000s into a strategy that was deployed on nearly a third of all balls in play in 2016:

The shift’s popularity has exploded since 2011, with each subsequent season setting new records for how frequently it was used. But given all of this shifting, it’s fair to wonder when the tactic will reach its peak — when hitters will have adjusted enough to keep the defense honest by, say, going to the opposite field, or hitting more fly balls, or even dropping down bunts.

We probably aren’t there yet. Even though the league’s batting average on balls in play (BABIP) has stayed relatively constant despite the ridiculous uptick in shifting, there’s also evidence that the shift has hampered the production of the players who face it the most. Then again, Cubs manager — and former shift-master — Joe Maddon used the tactic less than anybody else last season, instead employing a pitching staff who induced unusually soft contact to allow the league’s lowest BABIP. If the rest of baseball ends up copying the champs, maybe the shift will reach a high-water mark after all. –Neil

Are the kids still all right?

Kris Bryant burst into baseball in 2015, performing like an All-Star right out of the gate and earning Rookie of the Year honors at age 24. He improved in 2016, elevating his on-base percentage and isolated power on the way to being crowned the National League’s Most Valuable Player (not to mention leading the Cubs to their first World Series title in 108 years).

Bryant was emblematic of a larger trend in baseball: the rise of a new generation of talent. Driven by Bryant, Carlos Correa, Francisco Lindor, and a host of other exciting rookies, 2015 featured the lowest average age (weighted by production, as measured by FanGraphs’ wins above replacement) in more than three decades.

But that trend was not to last. The WAR-weighted age ticked upward in 2016, caused in part by the aging of that young cohort. It still remained the second-lowest figure in 30 years, but the abrupt increase suggests that rather than a general youth movement, baseball may have experienced a one-time spike in young talent, one that may lead to a golden generation.

The next couple of seasons should provide some clarity. If another class of rookies starts accomplishing amazing things, then perhaps baseball has made a long-term shift toward younger players. In contrast, if Bryant, Lindor, et al. remain dominant, then maybe 2015 was a unique event, the arrival of a new wave of great players who will drag the production-weighted average age up as they get older. Either way, baseball fans are witnessing a major shift in the game’s talent. –Rob

Is the bullpen takeover here to stay?

Postseason fads — which often replicate whatever novel development some team rides to the World Series — are usually quickly dropped in subsequent seasons. (Remember when we thought MLB would be overrun by a horde of speedy, contact-hitting Kansas City Royals clones two Octobers ago?) But last fall’s bullpen craze might be a rare playoff trend with staying power. That’s because the Cubs and Indians’ dominance in relief was just the most visible manifestation of a pattern that’s been building for years.

Over the past couple decades, bullpens have become central to teams’ plans. Relievers pitched 33 percent of available innings in 1997; that number reached an all-time high of 37 percent in 2016. More importantly, relievers also generated 24 percent of all pitching wins above replacement (WAR) last season, the most they’ve ever contributed. The latter number has been growing fast in recent seasons, up from just 16 percent as recently as 2005:

It’s long been known that a pitcher is more effective out of the bullpen than as a starter, so it’s not too surprising that by shifting a greater share of the workload to relievers, managers have gotten more value out of their ’pens. But the gap in effectiveness between the two types of pitchers is also growing at an incredible rate. In 1995, the first season of the post-strike era, relievers and starters posted basically identical fielding independent pitching (FIP) rates. Since 2012, however, the average FIP for relievers (3.79) has been 0.25 points lower than the average for starters (4.04).

That quarter of a run quickly begins to add up to wins, especially as relievers are called upon to pitch more and more — and, increasingly, in more important situations. Toss in the fact that there are more hard-throwing relievers than before, as well as more managers like Cleveland’s Terry Francona — who experimented with the kinds of revolutionary bullpen tweaks SABR-heads have been advocating for decades — and we might find ourselves looking back at 2016 not as the year relief pitching peaked, but rather as just another waystation on the road to total bullpen dominance. –Neil

Can we finally measure defense?

Since the inception of sabermetrics, defense has always stumped the statheads. Without the detailed data — like pitch location and exit velocity — that’s available to measure pitching and hitting, defensive metrics have been unreliable and inaccurate. Adam Eaton was one of the best fielders in baseball in 2016 … and, according to those same metrics, a below-average defender in 2015.

But the future of defensive stats looks brighter: MLB’s new Statcast system can measure everything about a defensive play, from the running speed of the fielder to the exact landing point of the ball. Armed with that new data, MLB’s statisticians have crafted impressive new metrics to quantify the difficulty of every outfield catch over the last two seasons, a huge upgrade on the information we had available before. (Kevin Kiermaier, your Gold Gloves appear to be well deserved.)

Still, the stats aren’t perfect. They don’t account for the direction the fielder has to run in, which means that they treat running forward the same as backpedaling. They don’t incorporate any information about an outfielders’ throws, so a strong and accurate arm counts for nothing. And they are only available for the outfield. Statcast still has major issues tracking grounders (losing as much as 20 percent of all balls in the dirt), so for now, the much more complex mystery of infield defense remains unsolved.

Perhaps the biggest problem with these defensive statistics is that they are not being released in full to the public. While MLB is providing snippets of the data in leaderboards and tweets, the complete data set is being kept under wraps. Front office insiders I’ve spoken to have pointed to issues with the data’s quality and the influence of teams eager to keep their analytics edge as two barriers to the data set’s full release. At a crucial point in Statcast’s development, it’s reasonable to wonder whether the data stream will eventually become fully public (like PITCHf/x) or whether it will remain a tool primarily for the front office (like the NBA’s SportVU camera system). –Rob

Is the Tommy John era over?

Two years ago, we were in the midst of a Tommy John epidemic. Elbow ailments felled major stars like Yu Darvish and laid waste to pitching staffs. But last year, Ben Lindbergh and I noted that Tommy John surgeries had suddenly dropped. And so far this spring — usually the most active time for players to be diagnosed with elbow issues — the scourge of Tommy John has become almost a nonissue.

Just when it seemed like Tommy John surgery was becoming a generation-defining problem, it has almost disappeared. Many of the ace pitchers who lost a year to the ailment have returned in force, including Darvish, who has regained most of his efficacy. Even when pitchers suffer ligament damage, doctors are increasingly prescribing less disruptive treatments than the operating table.

In prior eras, when one pitching injury died down, another one appeared. Before Tommy John, there were more severe shoulder injuries, which claimed many a young pitcher’s career. With one problem solved, we could be waiting for another crisis to begin. But let’s take a rare opportunity to be optimistic: we could be entering a new golden era of pitcher health! Back to the pessimism: That notion should frighten MLB’s hitters. If pitchers don’t need to worry about their shoulders or their elbows, they could dominate hitters like never before. –Rob

Will rule changes really speed up the game?

MLB unveiled some controversial rules changes this offseason, primarily targeted at speeding up the pace of the game. A couple of new wrinkles concern replays: managers will have only 30 seconds to decide whether to call for a replay, and reviews will be capped at two minutes. The most significant alteration eliminates the ritual of the intentional walk, requiring only a hand signal to send the batter off to first base.

The impact of this rule change will be minor because intentional walks are already uncommon and becoming more so. The same goes for the new replay rules, which might shorten a handful of interminable delays per season, but won’t affect most umpire reviews, which don’t last long enough to run into the new restrictions.

The real objective in these changes is Rob Manfred’s crusade since becoming commissioner: to speed up the pace of game. But if that’s the goal, Manfred is focused on the wrong things. Since 2008, most of the slowdown has come from players taking their sweet time between pitches, not uncommon events like replays and intentional walks. To truly pick up the pace of play, the commissioner will likely need to deploy an even more radical solution, like adding a pitch clock. But doing so would require the cooperation of the players’ union, which doesn’t want to disrupt the current pace. As a result, Manfred will likely have to chew on the edges without ever solving the underlying problem. –Rob

Will the offensive renaissance continue?

The long ball is back. In the last two years, offense has spiked from a three-decade low, a surge powered almost entirely by home run rates reminiscent of the Steroid Era. And no one is sure why.

There are theories. Some have proposed that players are attempting to hit more fly balls, which are more likely to get over the fence. Others have suggested that players are using more granular data to improve their swings. But most explanations don’t survive scrutiny.

In a series of articles, Ben Lindbergh and I developed the theory that a different ball is the source of the offensive spike. If a juiced ball is to blame, then MLB’s offensive explosion ought to continue. And since MLB Commissioner Rob Manfred has made it a priority to increase offense in the league, runs per game may soar even higher. Still, without knowing definitively why offense has spiked, it’s impossible to say whether the trend will continue. –Rob

Is pitch framing still worth anything?

Pitch framing was once a darling of sabermetrics, a stat and a method by which catchers could prove that they provided more value to their teams than the guys competing for their roster spots. For many of those catchers, all those frames add up to several wins over the course of a season. At least, they used to. Pitch framing might be be losing its value.

In recent articles, Fangraphs’ Jeff Sullivan has argued that as more teams have exploited pitch framing, the gap between the best and worst catchers has shrunk. With no absolutely terrible receivers in baseball any more, the average framing skill jumped and the value of being a great framer has declined. Paradoxically, all the attention paid to the significance of pitch framing has made it less significant.

In hindsight, the demise of framing seems inevitable. Modern front offices eagerly target undervalued skills until they aren’t undervalued anymore. Once they discovered framing and learned to target or develop the skill, it was only a matter of time before most catchers in baseball became good at it. Rather than being a bonus, pitch framing is now a prerequisite. –Rob

Is MLB’s era of parity over?

We tend to think parity in sports is a good thing. A more level playing field means a higher chance that any team could win, after all. But there’s a fine line between a league with a healthy competitive balance and one where every team is just plain mediocre.

For a long while, MLB was slouching toward mediocrity — or at least uniformity. In 2014, 23 of the 30 MLB teams won between 70 and 90 ballgames, a relatively narrow range differentiated only by an extra win every 9 days or so. Things got even more compressed in 2015, when a third of the league squeezed itself between 76 and 84 wins, which is far more teams around .500 than usual and indicative of a broader trend in baseball: The spread between the best and worst teams had shrunk rapidly, hitting its lowest level in decades. We can illustrate this by tracking changes in the standard deviation of wins (and wins above replacement) over time — essentially measuring how compressed the range of talent across the game has been.

This trend had a number of consequences, including making the sport less predictable and allowing luck to play a larger role in the outcome of the season.

But 2016 was the year baseball may have begun to swing back in the opposite direction. Last year, far fewer teams were stuck in that middle range of wins compared to the previous two seasons. More clubs were either clearly good or clearly bad — as symbolized by the symmetry of a league-best 103 wins for the Chicago Cubs and league-worst 103 losses for the Minnesota Twins.

Moreover, the correlation between payroll and wins (or WAR) in 2016 was easily the highest it had been for MLB since the late 1990s. Back then, the relationship between money and wins triggered a moral panic of sorts in the commissioner’s office, so it remains to be seen whether a similar crisis will emerge again 20 years later. But last season’s strong correlation — in conjunction with 2017’s unusually top-heavy projected standings — suggests that teams are getting more of what they’re paying for now than they have in a while, and we’re probably due for less parity as a result. –Neil