xBB% and Potential Pitcher Walk Rate Improvers

Three years ago, I introduced the best pitcher expected walk percentage formula yet. The formula uses a pair of strike type rates found at Baseball-Reference.com, including a pitcher’s in-play strike percentages, as well as his overall rate of strikes thrown. The beauty of the equation is that it uses components that stabilize quickly, as the rates are per pitch, rather than per inning or per batter. The equation isn’t nearly as strong as my xK% one, as it’s clearly missing sequencing, which may or may not be a consistent skill. But it’s pretty darn good and the best we have at the moment.

I calculated the xBB% marks for all qualified starting pitchers, compared it to their xBB% marks, and sorted. Let’s discuss those with the most significant potential for improvement as suggested by xBB%.

Potential Walk Rate Improvers

Name	SIERA	BB%	xBB%	Diff
Yordano Ventura	5.90	17.6%	13.0%	4.6%
Jeff Locke	5.00	13.0%	9.9%	3.1%
Jaime Garcia	3.20	9.2%	6.7%	2.5%
Jon Niese	4.64	9.1%	6.9%	2.2%
Sonny Gray	4.07	10.5%	8.4%	2.1%
John Lackey	3.34	6.3%	4.3%	2.0%
CC Sabathia	4.76	10.4%	8.5%	1.9%
Jose Fernandez	3.14	11.3%	9.5%	1.8%

I discussed Yordano Ventura last week as a potential strikeout rate surger. Despite landing on what is normally a positive list, I took the opportunity to point out my serious concerns about his health. Since that post, he issued another five free passes after facing just 22 batters, for a 22.7% walk rate in the game. He has now walked 11 batters in his last two games and already has a pair of six walk efforts. Of course, my xBB% metric suggests it shouldn’t be this bad, but even a 13% walk rate is terrible! Given his history of elbow issues, I would be absolutely shocked if he didn’t find himself on the disabled list soon. Something is clearly not right here and it seems like there should be a bigger deal being made out of it.

Jaime Garcia’s rate of strikes thrown is right in line with his previous two seasons and just a step below his two seasons before that. Yet his walk rate sits at its highest mark since 2010, tied for his career high. His velocity has been good, he’s induced his typical high rate of grounders, and he’s making batters swing and miss. There should be no need to worry about his control and for as long as he remains healthy and on the mound, he’ll be a valuable contributor in all formats.

So much for the Ray Searage effect on Jon Niese. Maybe it will eventually bear fruit, but so far nothing has improved. His strike percentage sits at a career low, but it’s not off enough to justify such an increase in walk rate. Yet even if his control improves, his low strikeout rate caps his fantasy potential.

Breathe easier Sonny Gray owners. His xBB% is just a touch higher than previous years and knowing improved control results are on its way means there should be less concern moving forward. The problem has been that his typically low BABIP has reversed course and jumped above the league average while his HR/FB rate has just about doubled. He’s another good example of precisely why I posted this.

Man, a pitcher with a 6.3% walk rate should have an even lower mark?! That’s what xBB% suggests for John Lackey. The 37-year-old continues to amazingly avoid the effects of aging, as his fastball velocity has essentially remained stable since 2009. In fact, his fastball has sat in a tight range between 91.4 mph (this year) to 91.7 mph during that time. That’s pretty remarkable, considering pitchers are expected to lose velocity every single season.

We’re always concerned about a pitcher’s control when he returns from Tommy John surgery, but we assume that the following season, that pitcher will be back to normal. So far, Jose Fernandez has endured the opposite effect — last year, his strike rate was elite. But this year, it has tumbled four percentage points, which is quite drastic. His velocity is down a notch, but he’s still generating loads of swings and misses, so his stuff is clearly fine. But you have to wonder about the control, even though xBB% suggests it shouldn’t be as bad as it has been. Even a 9.5% walk rate is far worse than expected. You also wonder how a guy with his repertoire has allowed an insane 30% line drive rate since last season. There must be some bad luck involved in there, but it certainly explains the inflated .349 BABIP. I’d be a a bit nervous if I were a Fernandez owner as something might not be right here.