It is time to talk about San Diego’s most exciting hitter. He’s young and he can hit dingers.

That’s right, I’m talking about Franmil Reyes! If you thought that I was talking about Manny Machado or Fernando Tatis Jr., then maybe take another look at the title of this article. Reyes is a fascinating player in that he can hit home runs, but for some reason almost all of them come without a runner on base. He has hit 24 career home runs, and 18 of them have been solo shots. He has only 42 career RBI; among all players in major league history with at least 24 home runs, those 42 RBI are the fewest. And it is not because he pinch hits. In fact, only one of his home runs came when he did not have multiple plate appearances, and that home run was a two-run shot.

Perhaps this is just a fluke. After all, the Padres had a major league-worst .297 OBP last season, and this season has not been any better (through yesterday, they’ve been good for .287 – 28th in baseball). But Reyes’ ability to hit home runs is no fluke – this season, his average exit velocity is 94.0 mph (12th in baseball) and his barrels/PA% is 12.8% per Statcast (tied for eighth in baseball with Christian Yelich). In addition, his contact rate seems to keep improving.

I have a theory to explain Reyes’ numbers: With his power, who cares if there are any runners on? He has the potential to hit one out every single plate appearance, so he might as well swing for the fences every time. But Reyes is not the only one who appears to be hitting more solo shots – it is a trend that is going up in baseball.

In 2014 the ball was not going out, and isolated power was way down. The major league wide average has fluctuated over the years; isolated power is even higher than it was in the early 2000s, and currently higher than in 2017. (The ball appeared less lively in 2018, but the early season numbers in 2019, and research into the ball, suggest that we’ve returned to a livelier ball yet again.) Although isolated power is higher overall, the numbers without runners on base have increased more than when runners are on base – the league-wide ISO with nobody on has increased from .161 in 2018 to .176 this season compared to .162 and .172 with men on base.

And while home runs have increased overall, it is important to note that the rate of solo shots is increasing at an even higher rate, and decreased at a lower rate last season:

Percent Change in Solo Home Runs Since 2014 Season Solo HR Solo HR – Prev. Season Percent Change 2018 3316 3603 -7.96% 2017 3603 3332 8.13% 2016 3332 2887 15.41% 2015 2887 2390 20.79% 2014 2390 2811 -14.97%

Percent Change in Total Home Runs Since 2014 Season HR HR – Prev. Season Percent Change 2018 5585 6105 -8.52% 2017 6105 5610 8.82% 2016 5610 4909 14.27% 2015 4909 4186 17.27% 2014 4186 4661 -10.19%

After a decrease in home runs in 2014, we saw a massive increase, which was a greater change than from 2016 to 2017 when baseball broke the season home run record. But solo shots went up at a greater rate than home runs with runners on – a 20 percent increase from 2014 to 2015. And we saw a larger increase from 2015 to 2016 as well. Although home runs went down overall from 2017 to 2018, the percent decrease in solo home runs was not as sharp as that of home runs in total – roughly 8 percent decrease for solo shots and 8.5 percent for total home runs.

Keep in mind that it is not as if on-base percentage is down compared to what league rates have been historically – in fact, it is up from last year (.318 major league average in 2018 and .334 in 2019). Players get on base at a similar rate compared to 25 years ago. And although the strikeout rate has increased, that is not as much of a problem here. In these situations, a strikeout is almost the same as a fly out or a ground out (assuming that there are no errors, of course).

Thanks to Baseball Reference, we can look at every home run and how many runners (if any) were on. I looked at the percentage of home runs that were solo shots in the live-ball era (since 1920), and solo-shot percentage appears to be a continuing phenomenon. If you are wondering what solo shots were like before 1920, it fluctuated by year. In 1881, 46 of the 76 home runs (60.5 percent) came without runners on, before decreasing to 44.4 percent the following season.

The percentage of solo shots has peaked in today’s era, in the mid-1950s, and the late 1960s. Over 60 percent of home runs have been solo home runs this season:

Highest Percentage of Home Runs Are Solo Shots Since 1920 Year Solo Total Pct. 2019 765 1272 60.1 2013 2811 4661 60.3 1968 1197 1995 60.0 2018 3316 5585 59.4 2016 3332 5610 59.4

And if you are wondering where the year of the home run falls: 59 percent of home runs were solo shots in 2017, which is eighth highest since 1920. Among the top five seasons in solo shots, four of them have come in this decade; the other came when hitting was so scarce that baseball lowered the mound the following season.

So how valuable is a solo shot? Mind you that it is still hard to hit a baseball into the stands – roughly three percent of plate appearances end in a home run this season. In addition, it is “only” one run, which could be as attainable as a single, a stolen base, and another single. Should teams attempt to put runners on and drive them in, or should they attempt to have most batters try to hit one out no matter what the situation is?

First, it is important to know that when there are no runners on base, a batter is more likely to see a fastball than if there were runners on:

Fastball Usage by Season Since 2015 Year No Runners Runners 2019 33.9 24.4 2018 35.1 25.0 2017 35.2 25.4 2016 35.4 25.8 2015 36.4 26.0

Yes, fastballs are down in general in the majors, but batters are likely to see a fastball 33.9 percent of the time when there are no runners this season compared to 24.3 percent where there are runners on. If more fastballs are being thrown when there aren’t baserunners on, why not try and attack more often in those situations?

If you are wondering about how Franmil Reyes does against fastballs, it is not bad at all. Last season, he hit .310 and slugged .545 against the fastball compared to .274/.500 against breaking balls and .161/.397 versus offspeed pitches. Although he is hitting .246 on fastballs this season, his expected batting average is .304. Similarly, his slugging is .561, but his expected slugging percentage is .675. Of those 24 career home runs, 15 have come off the fastball.

Is it possible that home runs are easier to hit when there is nobody on base compared to when there are men on base? With more breaking balls thrown with men on, it could be the case, which could result in hitting more solo home runs. We are still left with the same question, however. At the end of the day, what approach is more likely to get runs – is it trying to hit a home run every time, or is it trying to get on base and relying on your teammates to knock you in? Hence, is trying to hit a home run every time valuable? With nobody on base, it depends on how many outs are already in the inning.

I looked at this year’s run expectancy for our scenario for each possible number of outs in an inning. For example, with no men on and no outs, this season’s run expectancy is 0.53 runs. The run expectancy increases when you have more men on base, and decreases when there are more outs in the inning. This is baseball 101, just with numbers to illustrate the predictive outcomes.

With run expectancy, we can calculate the change in run expectancy from the scenario that the batter is in to the new scenario after the batter’s plate appearance. For example, if there is nobody on and one out, the run expectancy is 0.28 runs (notice that the run expectancy decreases by almost half when you get an out). Suppose then the batter hits a single, putting a man on first with one out. The run expectancy for that inning is now 0.53, so the change in run expectancy is 0.53 – 0.28 = 0.25. The formula is as follows:

Change in RE = RE End State – RE Beginning State + Runs Scored

If a batter hits a solo shot, the end state is the same as the beginning state, but now a run has been scored, so you factor that run in. Here is how each change in run expectancy happens based on each scenario and each hit. For simplicity, I looked only at singles and walks instead of adding in errors:

Run Expectancy with No One on Base Hit 0 Outs 1 Out 2 Outs Single + Walk .398 .249 .132 Double .600 .402 .224 Triple .829 .630 .267 Home Run 1.000 1.000 1.000

The run expectancy difference when hitting a triple with no outs is similar as hitting a home run, as there is still a high chance of scoring via a ground ball, fly ball, or hit. That, of course, changes significantly when there are two outs, as now a player must get a hit (or reach via an error) in order for the run to score. That is why the change in run expectancy is around the same with a two-out double compared to a two-out triple. Based on this chart, it seems obvious that ANY player should try to hit a home run with none on and two outs.

But it is easier to hit a single or draw a walk than it is to hit a double, triple, or home run, so we have to factor in the probability of each event occurring. I took the probability of each event as the current percentage of each hit over the total number of plate appearances, and multiplied it by the run expectancy difference. The rates are based on when there are no runners on base. Yes, there are other ways to get on base besides these, but let’s limit it to these five:

Run expectancy Difference * Percentage of Event, No One On Hit 0 Outs 1 Out 2 Outs Single + Walk .090 .056 .030 Double .027 .018 .010 Triple .003 .002 .001 Home Run .035 .035 .035

When there are no outs and nobody on, drawing a walk or hitting a single is still the preferred option. But that changes when there is only one out and when there are two outs. With two outs, the chances of getting a run with a home run are more likely than drawing a two-out walk or hitting a single with two outs. Oh yeah, and it is really hard to hit a triple, by the way.

Since there are more plate appearances when there is nobody on base compared to when there are runners on, and the chances of getting a run with a home run are higher than almost any other scenario, then it is logical for teams to try to hit a home run each time, especially if it is with a hitter that can hit a decent amount of home runs.

Which brings us back to our most exciting player, Franmil Reyes! He is contributing more to the team’s run support a lot more than with runners on, as if he (or the team) knows that the team’s run expectancy is higher when he is batting with nobody on. Based on Statcast data, his expected wOBA is much higher in scenarios with no runners. Among players with at least 100 plate appearances in each split since last season, Reyes has one of the largest differences:

Franmil Reyes is just one of many players with the type of pop to hit a home run often, so why not attack with no runners on, especially if pitchers might throw him a fastball more often with nobody on. Based on his 24 home runs and 18 solo shots, and with a team that does not score often, that may be its plan of attack. With power like Reyes’, if you are going to swing, you might as well swing for the fences, even if nobody is on base. Chicks did the long ball, and so do mathematicians.

A few other things to consider:

Clearly, we are looking at the majors as a whole for these scenarios, and although I used Franmil Reyes as an example, it would be interesting to see what, if any, other hitters are better off trying to hit a home run with nobody on vs. just trying to get on base. Does this affect players who are shifted against most, for instance?

Players who bat in the leadoff spot are guaranteed to have at least one plate appearance per game with no one on. Some players, like George Springer and Joc Pederson, have had great success hitting leadoff home runs. Does this data suggest that there should be a power hitter batting first? Should Franmil Reyes lead off?

References and Resources