xBB% and Potential Pitcher Walk Rate Regressers

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. Yesterday, I discussed the group of starters with the most significant potential for improvement in their walk rates. Today, let’s discuss those with the most significant potential for regression as suggested by xBB%.

Potential Walk Rate Regressers

Name	SIERA	BB%	xBB%	Diff
Taijuan Walker	3.05	2.3%	7.8%	-5.5%
Jake Odorizzi	3.80	4.9%	9.6%	-4.7%
Luis Severino	3.67	4.3%	8.1%	-3.8%
Mike Fiers	3.80	2.8%	6.6%	-3.8%
Jose Quintana	3.38	5.1%	8.3%	-3.2%
Tyler Chatwood	3.84	5.3%	8.4%	-3.1%
Rick Porcello	3.09	5.1%	8.0%	-2.9%
Josh Tomlin	4.03	1.7%	4.5%	-2.8%
Jerad Eickhoff	3.45	4.6%	7.2%	-2.6%
Chris Sale	3.31	5.3%	7.9%	-2.6%
Collin McHugh	4.14	5.1%	7.5%	-2.4%
Matt Moore	3.49	6.5%	8.9%	-2.4%

I like Taijuan Walker and this may very well end up being his breakout year, but it’s probably going to be because of the ground ball rate surge and a simple reversal in fortune. His strikeout rate is identical and xBB% suggests his walk rate should actually be higher than last year. There’s an easy story here of the hyped young starter who disappointed last year and is putting it all together this year. That makes him a great candidate to sell high on, though your potential return will obviously decide whether it’s worth pulling the trigger.

What happens when your strike percentage falls by two percentage points? You shave one a half points off your walk rate, of course! Everyone knows that throwing fewer strikes results in better control, right? Well, not exactly, but that’s what has happened for Jake Odorizzi. His underlying skills are almost identical to last year, save for the improved walk rate. But that is in no way supported by his strike rate. Expect that 3.10 ERA to rise.

If it wasn’t enough that Luis Severino has an ERA over 6.00, he should be allowing even more base runners! He’s getting bitten by the luck dragons on all three fronts, which could either mean he’s simply not Major League material at the moment, or he’s a super buy low. I would be more confident if he was generating more whiffs. I’ll still buy in deep mixed and AL-Only leagues, but would shy away in shallower formats.

Despite Mike Fiers‘ appearance here, I’ll be one annoyed owner (in two leagues!) if he’s the one to head to the bullpen upon Lance McCullers‘ return from the disabled list. After last night’s start and Scott Feldman following Fiers in relief, it would seem he’s going to stick in the rotation.

Jose Quintana’s appearance marks just another reason why I’m not so high on him and he remained stagnant in my latest tiers update. He’s doing nothing differently this year than in the past, aside from throwing fewer strikes, inducing fewer ground balls, and allowing more line drives and hard contact. In fact, he actually seems like a worse pitcher! If anyone in your league feels the opposite way and you’re lucky enough to be an owner, take advantage.

It might not take much longer for Chris Sale and the White Sox to realize this supposed pitch to contact strategy is not going to pay off. He’s throwing fewer strikes and getting fewer swings and misses. How can that possibly sound like a good idea?

Even given Matt Moore’s appearance here, I’m rather bullish on his prospects. That xBB% is still much improved from his two full seasons back in 2012 and 2013, while his fastball velocity is at its highest since 2012. He’s getting hurt by an inflated HR/FB rate, which has in turn suppressed his LOB%. It’s masking an excellent skill set that represents a strong rebound to healthier days. He’s not going to throw a whole lot of innings, but he should be very good when on the mound. He’s the only true strong buy on this list.