Using xwOBA to Explain Alec Bohm’s Slump

Exit velocity. Launch angle. Claim you’ve never heard these terms? You’re lying!

Since 2015, all 30 MLB stadiums have been fitted with sensors which track all player and ball movement. This system is called StatCast and it’s awesome!

StatCast tells us how hard batters hit the ball (exit velocity). It tells us how fast baserunners or fielders are moving. It can even use the angle that the ball is hit off the bat (launch angle) along with the speed of the hit to project how far a homerun would have traveled if it didn’t hit that light tower.

The coolest offensive application of StatCast data is to determine how lucky or unlucky hitters have been. StatCast can tell us how likely a given batted ball is to result in a hit.

Say a hitter mashes a ball at 95 MPH with 10.2º launch angle. StatCast will look back at all the other similar batted balls and determine how often these resulted in hits. Not only that, but StatCast can tell us the likelihood that a given batted ball results in a single, double, etc.

This has created a new sabermetric – xwOBA. xwOBA is a variant of wOBA – which may also be new to some fans. wOBA stands for Weighted on-base Average and assigns weights to different hits (triples worth more than doubles for example) while also assigning value to walks, hit by pitches, RBIs, runs, etc.

The result is a percentage stat (like batting average) out of 1.000 which attempts to quantify a hitter’s ability at the plate. Note that wOBA disregards baserunning as does xwOBA.

xwOBA stands for Expected Weighted on-base Average and uses StatCast data to determine what a hitter’s wOBA should be.

For example, a batter might crush a ball into the gap which normally results in a double or triple. The outfielder makes a terrific sprawling play and turns extra bases into a flyout. The hitter’s actual wOBA will take a hit but his xwOBA will reflect the tremendous contact that would normally result in extra bases.

Using xwOBA to analyze hitter performance is relatively simple. If a hitter’s xwOBA is much higher than his wOBA – he is getting unlucky. A low xwOBA means a hitter is benefitting from some poor defense or bloop hits.

Batting average and OBP are so variable and do not always reflect hitter performance. Let’s take a look at the sabermetrics and see what we can dig up!

Alec Bohm is Having a Much Better Season Than You Think

#3-overall pick in 2018 of the Phillies Alec Bohm is mired in a deep slump in 2021. Bohm excelled in the short 2020 season and has been given first-team reps this year … only with far inferior results.

Bohm was graded a 55-contact hitter with 60 raw power but only 45 in-game power as a corner infield prospect. Unable to translate his cage power into games, Bohm worked to become a line-drive oriented singles hitter which scouts described as a “3B/1B version of Michael Brantley“.

In 67 games in 2021, Bohm has played third base in 65 of them – playing first base just twice. Here are the fantasy stats for Alec Bohm to get a feel for his production. We’ll dive into sabermetrics next.

Year	G	PA	BA	HR	RBI	R
2020	44	180	.338	4	23	24
2021	65	253	.230	4	29	26

Obviously the batting average is over 100 points lower in 2021. Bohm’s production is also down, as his HR, RBI, and R numbers are nearly identical to his 2020 outputs despite 50% more plate appearances.

So what’s going on? Is Bohm a dud? Let’s not label him so quickly. There is a lot going on under the hood which deserves our analysis. Personally, I own Alec Bohm in my fantasy keeper league so I have a vested interest in finding the root cause of his slump.

To begin, let me throw in some non-fantasy stats that help tell the story of Bohm’s plate appearances.

Year	BB%	K%	BABIP	wOBA	xwOBA
2020	8.9%	20.0%	.410	.381	.357
2021	5.5%	26.9%	.299	.257	.322

So what are we looking at here? Great question.

The BB% and K% indicate that Bohm is walking less and striking out far more in 2021 than he was in 2020. This is a big issue. Low walk rates – especially when combined with high K rates – are a red flag that a hitter is overmatched at the plate.

Now there are some hitters – Tim Anderson and Javier Baez come to mind – who can sustain high-K-low-BB approaches. These hitters are few and far between. Bohm’s minor league numbers indicate he is not this type of hitter.

Bohm was rushed through the minors – spending just 2 seasons between rookie ball, 3 different levels of A-ball, and AA before getting the call to The Show.

Bohm’s BB and K rates were very impressive in both A and AA play.

Level	PA	BB%	K%
A	391	10.0%	13.8%
AA	270	10.4%	14.1%
2020 MLB	180	8.9%	20.0%
2021 MLB	253	5.5%	26.9%

Yuck! Bohm went from great in these peripheral stats to a liability. What’s wrong with him? The numbers tell the story.

Bohm is hitting the ball with authority in 2021 – hard contact is not the issue. Bohm’s average exit velo of 92.3 MPH ranks 18th in the Major Leagues among qualified hitters.

With consistent good contact in 2021, Bohm’s xwOBA is in good shape – .322. .322 is not an awesome wOBA – in fact it is right around league average. Phillies’ fans (and fantasy owners) would love for Bohm to be league average right now, though.

Let’s put this in perspective: even with awful BB/K splits, Bohm is hitting the ball well enough to be a league-average hitter. This is immensely exciting!

The discrepancy between Bohm’s wOBA and his xwOBA is -0.065. This is a huge gap. In fact, Alec Bohm has the 3rd-largest discrepancy of any hitter within the top-50 in exit velo in the Major Leagues this year.

The kid continues to get unlucky. The manner in which Bohm gets unlucky must be insanely aggravating. Bohm’s average launch angle is super flat. Remember how I said he was working to hit more line drives? He is succeeding in that arena.

Bohm’s average launch angle in 2021 is a mere 5.1º – the 11th-lowest among all hitters in the league. This means that many of Bohm’s outs are hard liners speared by infielders and smashing one-hoppers right at someone.

Getting robbed over and over will take a psychological toll on anyone – let alone a 24-year-old first-round pick who was rushed through the minors and given a starting role in his rookie season.

Bohm’s well-hit balls will eventually start finding holes – this is not the main issue. Fixing the BB/K rate is Bohm’s main long-term concern right now. The encouraging thing is Bohm’s strikeout issues at the plate are far different from most young hitter’s issues.

How Pitchers Are Attacking Alec Bohm in 2021

Most young hitters receive a steady diet of fastballs upon entry to the league. The good ones mash these meatballs, forcing pitchers to switch to an all-offspeed attack. This is where many hitters struggle – some are incapable of making the adjustment, never having seen so many good offspeed pitches in their life.

The opposite has occurred with Alec Bohm. Check out these pitch charts. They show the frequency of different types of pitches that Bohm has seen over his 2 years in the bigs.

Year	4Sm FB%	Cutter%	Sink%	Slider%	Curve%
2020	32.5%	11.5%	18.8%	19.1%	8.3%
2021	38.4%	5.9%	17.8%	23.2%	5.1%

Feel free to check out the pitch distributions to other young hitters to see how atypical this approach is to Alec Bohm. Bohm saw many moving fastballs and curveballs in 2020 (cutters, sinkers) and is now receiving a diet of mainly straight fastballs with some sliders mixed in there to keep him honest.

Most young hitters struggle with chasing pitches outside the zone. Not Alec Bohm. In 2021, Bohm is having a hard time catching up to fastballs in the strike zone.

Z-Swing and Z-Contact are pitch info stats which indicate how often a batter offers at a pitch inside the strike zone and then how often he makes contact on those swings. Check out the numbers for Bohm.

Year	Z-Swing%	Z-Contact%	Swing%
2020	72.0%	87.9%	47.5%
2021	77.4%	82.4%	50.0%

Bohm is getting more straight (and hittable) pitches in 2021 but is missing them. His contact rate on pitches inside the strike zone has fallen drastically while his overall swing rate has risen a few percentage points.

So what does this mean? Give me something qualitative.

As a top-3 pick at just 24 years old (he turns 25 in August) Bohm is under a lot of pressure to perform out there. His abnormally lucky start (check out that .410 BABIP in 2020) has raised already lofty expectations – making his 2021 slump feel even worse.

Alec Bohm is still mashing the ball. This gives reason for optimism. Constantly hitting the ball right at defenders is hampering the confidence of the young Bohm, and he is pressing at the plate as a result.

Combining the BB/K data, the pitch selection, and his xwOBA tell me this: Bohm’s bat belongs in the top-third of all MLB hitters but his eye is not quite there yet. Poor luck at the dish this season has compounded a relatively minor setback.

As long as Bohm remains in a good frame of mind – he will become a top-50 hitter in this league within 2 years. I am not moving Bohm off my keeper league roster and neither should you!

See you on top, boppers!