Matt Wieters HR Hypothesis: Blame Millenial Pitchers' Lack of Self Control

Yesterday, I heard about Matt Wieters' hypothesis about why home runs are up to potentially record breaking numbers after years of power decline.  His thought was that pitchers were being aggressively promoted as a result of fastball velocity as opposed to being able to master command of their pitches.  In other words, pitch locations were wobbling well away from the intended target and getting clobbered.  Cynically, this would be an argument a catcher might make to explain why a pitcher is at fault with a focus on pitchers with no seniority.

To test better conceptualize that, I put together a series of graphs showing home run per fly ball rates from 2008 until 2016.  If mistakes are the issue, then one would expect an increase in that rate as more pitches are squared up on.  Second, if this was an age issue, then that would become evident.  Historically, there are no significant differences between age groups.

The above graph makes it clear that all age groups have seen a major increase in home runs per fly ball.  It simply is not a youth issue and one would suspect that very few players above the age of 31 are without much experience at the MLB level.  I next broke this out into starters and relievers (not shown).  The rate follow the same shape, but with relievers 0.5 to 1.0 % fewer HR/FL than starters.  No significant differences were found for any age group for either relievers or starters.

To gauge how much of an increase we are discussing here compared to the historical (2008-2015) mean, I graphed each age group and separated them by starters and relievers.

There is a U shape here where younger and older pitchers have been more aversely impacted with HR/FL increase in rates.  Again though, all groups have observed significantly higher HR/FL rates.

With these graphs in mind, it is difficult to see much beyond the Wieters' hypothesis about poorly experienced arms making everyone look bad (or good, depending on your point of view).  After writing this up, the Washington Post took some aims at answering whether Wieters was right.  They looked into whether more home runs are being hit (they are), whether fastball velocity has increased (it has, which we have known for quite a while and actually wrote the seminal piece several years ago on this site), whether more mistake pitches down the middle are being hit for home runs (yes, which tracks with more home runs overall being hit though), and whether young pitchers are at fault (not beyond historical norms).

While looking at the batted ball data, the differences are not much and do not appear to be significant.  However, it seems that this noisy data might suggest that there is more hard hit contact and that it siphoned it from the medium hit group.

Season	Soft%	Med%	Hard%
2008	17	56	27
2009	16	57	27
2010	18	52	30
2011	24	52	24
2012	16	56	28
2013	17	53	30
2014	18	53	29
2015	19	53	28
2016	19	50	31

 Maybe this means that players are squaring up on the ball better.  I do not know.

Another idea is that perhaps teams are embracing more uppercut style hitters as the league embraces more groundball pitching.  How does that pan out?

Season	LD%	GB%	FB%
2008	20	44	36
2009	19	43	38
2010	18	44	38
2011	20	44	36
2012	21	45	34
2013	21	45	34
2014	21	45	34
2015	21	45	34
2016	21	45	34

 Honestly, if you had told me that the last five years have resulted in a leveling off of batted ball profiles and that we are seeing levels lowers than the pre-PED testing era.  All in all, I am at a bit of a loss.  Perhaps teams and players are more effective with changing swing planes, but I am doubtful of that.  Perhaps the ball is both legal and accidentally a little juiced this year.  Regardless, I do not think Wieters' hypothesis about millennial pitchers works.