As we all sit and overanalyze spring training at-bats and pitch mixes, it's important to remember that the small sample sizes of a few half-games against essentially AAAA talent can often be misleading. Instead, I find it's far more telling to use late-season changes from the year before to try to identify who has made clear strides or changes in approach.

Those changes provide us a foundation of MLB-level success to build off of but can often portend an offseason spent working and focusing on a particular philosophy or mechanical adjustment for even more potential growth.

Today we're going to look at players who experienced major power growth in the month of September last season that I believe could lead to legitimate sustained growth and (varying degrees of) fantasy relevance in 2020.

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September stats: .259/.319/.647, 10 HR, 20 RBI, 16 R, 1 SB

I covered Brett Gardner just last week in a piece on increased launch angles, but it's pretty clear that the veteran left-hander is trying to re-invent himself as his speed begins to dry up. He hit only 11 home runs in the entire first half of 2019, but it's clear that he made a conscious launch angle adjustment in the middle of the summer.

On July 4, his average launch angle was under eight degrees, and he had spent much of the first half of the season under the MLB-average launch angle. Once he raised his launch angle above that average mark on August 5, he basically never fell beneath it again. As a result, his doubles (10 in August with three home runs) turned into home runs (three doubles in September with 10 home runs). To me, that signals a clear philosophical change that allowed Gardner to take advantage of the short porch in right at Yankee Stadium.

While most projection systems think Gardner's home run total will be cut in half, down to around 14, I believe that's foolish. I am buying into his second-half change and consider a 20-10 season seems well within reason. This is an obvious buying opportunity.

September stats: .378/.472/.744, 9 HR, 20 RBI, 24 R, 3 SB

Meadows' power spike was more in the second half of the season than just September as he also hit eight home runs in August. In checking his rolling averages on Statcast, there isn't a lot that stands out in terms of adjustment, except his K%. In June, his worst month, Meadows' K% spiked to 40% and spent most of that month just under 30%. His K% increased to 30.4% in July before dropping to 18.3% in August and 15.1% in September.

Between a thumb injury at the end of April and a rough stretch in June, it's clear that Meadows hit a rough patch as pitchers adjusted to him or he had to adjust his swing to compensate for the injury. However, the rolling charts suggest that he made an adjustment towards the end of the summer. Considering this was Meadows' first year with over 200 at-bats at the Major League level, it's likely that he simply got more comfortable with major league pitching as the season went on.

As a result, I believe Meadow's second half was less of a surge and more an instance of a young player adjusting to the MLB level. Considering the impressive quality of his second-half (.291/.364/.619 21 home runs, 48 RBI, 47 runs) him being able to carry it over into a full season would provide another level of fantasy goodness for the young star.

September stats: .261/.337/.648, 9 HR, 25 RBI, 18 R, 3 SB

Listen, I swear that I'm not forcing Odor into all of these articles. He's showing up here on his own, which is only increasing my need to draft him on nearly every team that I have. However, this wasn't simply a final-month development. Odor's September was eerily similar to his July, as he posted a .264 average in July and .261 in September. He also hit eight home runs and knocked in 25 runs in July, while hitting nine home runs and driving in 25 runs in September. So what happened in August that ruined a full second-half breakout?

Right off the bat, his .190 BABIP stands out as being particularly flukey. Also, his K% was at its lowest point ever early in August and his BB% jumped to nearly 14%, which would easily be a career-high. Those numbers indicate that, in addition to getting unlucky on batted balls, Odor was trying to be more patient at the plate and perhaps being too passive.

What's interesting to me is that he appeared to find a sweet spot in the plate discipline in September where his K% dropped below 30% for almost the entire month (ending at 27.6%) but his BB% leveled out at 9.2% which is a marked improvement from his career numbers. In fact, his 10.2 BB% for the second half of last season easily marks a new level for the 26-year-old.

Early September also saw Odor notch his lowest exit velocity over an extended stretch before getting back to career marks around the middle of the month. Since Odor's BB% has been rising over the last three years, it seems as though he has been making a conscious effort to control the strike zone and perhaps found a strong balance at the end of the season. The fact that he hit nine home runs without his career average exit velocity tells me that there could be more growth to come if his plate discipline mentions.

I'm too far in now not to be buying this as improved plate discipline with a potential power spike on the horizon.

September stats: .347/.441/.693, 8 HR, 19 RBI, 25 R, 3 SB

Much like Meadows, this wasn't really growth for Semien as much as it was consistency over the second half of the season. He had eight home runs in August and six in July, so the September power was present for much of the second half of the season. He did see a major uptick in his batting average in September, in part because he compiled a 13.6 BB% and a minuscule 10.2 K%. Those were improvements from the 10.6 BB% and 17.1 K% in the month of August, but his 12.6 BB% and 12.6 K% numbers from July would suggest that August was more of an outlier than September.

The overall improvement in plate discipline over the course of the season matches his season-long decrease in O-Swing from 26.2% in 2018 to 23.1% in 2019. As he controlled the strike zone better, he likely got better pitches to hit, which is why the second half of his season demonstrates more consistent Hard Hit% and Sweet Spot%.

Overall, I'm not sure that Semien made any massive change to his performance or underlying metrics in the final month of the season. However, I see a veteran hitter continuing to iron out his weaknesses and make himself into a high floor player with few offensive weaknesses. As a result, it's quite possible that we see something similar to Semien's second-half metrics over the course of the full 2020 season, which could look something, in the best case, like .290/.396/.600 with 30 home runs, 90 runs, 80 RBI, and 10 stolen bases. That makes him great value at pick 90.

September stats: .220/.234/.582, 8 HR, 20 RBI, 13 R

I've always considered Grichuk the epitome of empty home runs. Even the stat-line above is a perfect encapsulation as a .220 average could crush categories in roto leagues if it wasn't properly balanced by other players. Much of my concern for Grichuk stems from his poor patience and plate discipline. He has a 5.8% career BB%, and he finished September with a 24.5 K% and just a 1.1 BB%. Those are terrible numbers any way you slice it. In fact, Grichuk's O-Swing% went up in 2019, which gave me even more cause to doubt him.

However, a look under the hood was a little more interesting. Despite Grichuk's O-Swing% going up, his O-Contact% went up over 5% and his Z-Contact% also went up, which says that Grichuk was making more contact in general. Noticing his .197 BABIP in September also suggests that his low batting average during the month was a little unlucky. A point that his xBA seemed to agree with.

For almost all of September, Grichuk had a league-average xBA, and his xBA numbers in August, where he hit .255 with six home runs, were well above average. Since Grichuk's career BABIP is .295, it follows that his .197 September numbers and .266 numbers on the season should regress to the norm. Again, an idea that his x-stats support. Thus, it seems entirely feasible that Grichuk, who is locked into consistent at-bats in the Blue Jays' lineup, should hit closer to his .244 career average, with consistent 30 home run power that is supported by a late-season adjustment to his launch angle.

All of which makes him worth buying into if you need power late in your drafts. Just make sure you've drafted enough batting average first to offset the slight hit he'll inflict.

September stats: .291/.359/.612, 7 HR, 15 RBI, 22 R

Something changed with Starlin Castro in August. It's obvious from the performance. He had eight total home runs when the month of August started. He hit seven in August and another seven in September. He batted .245/.272/.336 in the first half of the season and .302/.334/.558 in the second half. The difference is clear enough that we need to take note. But why did it happen?

For starters, his launch angle changed in the second half of the season, putting him above the league average and around a minimum of 15 degrees for much of the month, an optimal angle for home runs.

He started to hit the ball slightly harder, but nothing he hadn't done before for stretches.

His K% was largely unchanged and still below the MLB average. His BB% spiked for a bit but was still relatively non-existent. So it was hard to immediately lock down a specific change in Castro except for the slight shift in launch angle.

Then, I stumbled onto this quote from his teammates Miguel Rojas: "Mechanically, he made just a little adjustment to drive the ball more in the air instead of hard ground balls...And if you ask him, he changed his bat. So after changing his bat, he started feeling much better about himself at the plate. Those are the kind of things in the middle of the season, when you’re not having a good one, you change your bat and all of a sudden you start hitting the ball well.”

Boom. We have a conscious mechanical adjustment but also a bat change which would presumably allow him more ability to control the bat head on its new path. These two things are sustainable changes, not flash-in-the-pans.

It should be noted that Castro's xBA dropped below .250 for much of September, despite the .291 average he put up, so some regression in the average department should be expected. However, he's moving to a better hitter's park and hitting in a stronger lineup, so if he takes these bat and launch angle changes with him, we could be looking at sneaky good value for a MIF option with multi-position eligibility.

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