In an interview with Jon Meoli, Chris Tillman argued that his improvement is due to throwing his off-speed pitches for strikes. The data I’ve seen (downloaded via ESPN Stats and Information) suggest that this is indeed a factor. He’s been able to throw his curve and slider for strikes more often and therefore has forced batters to swing more frequently. As a result, his curve and slider have a combined swing-strike rate of 13.1% compared to his 2013-2015 rate of 6.6%. In addition, his changeup has been deadly against left handed batters. This helps explain why his strikeout rate is at 24.2% compared to last years’ 16.2%. More strikeouts typically result in better performance. This chart shows his basic performance.
Furthermore, batters are doing roughly the same amount of damage on balls put into play as they’ve done in previous years. When putting the ball into play, opposing batters have a .266 BABIP against him, a .355 wOBA and a 4.5 HR% in 2016 compared to an .277 BABIP, .355 wOBA and 4.1 HR% from 2013-2015. In addition, his walk rate has increased from 8% in 2013-2015 to 9.1% in 2016. The sole area where he’s improved seems to be strikeouts. In part, I definitely agree with his assessment.
However, the change in his performance comes into better focus when we look at his performance based on whether runners are on base. His strikeout rate with the bases empty is 24.4% in 2016 compared to 17.6% from 2013-2015. This year’s rate is easily the best of the four. However, his wOBA is .334 in 2016 and just .320 in 2013-2015, suggesting that his performance is worse this year than in previous years. This can be explained by the fact that his BABIP from 2013-2015 with the bases empty was .269 compared to this years’ .297.
Tillman has improved with men on base. When there’s only a runner at 1B, opposing batters have a .247 wOBA against him in 2016 compared to a .338 wOBA from 2013-2015. This is in part due to the fact that he has an 28.8 K% and 5.1 BB% in 2016 compared to a 16.3 K% and 7.2 BB% from 2013-2015. But it’s also in part due to a .222 BABIP in 2016 compared to a .293 BABIP from 2013-2015. This explains why his wOBA in play for these situations was .373 from 2013-2015 but .310 in 2016. Certainly, he’s doing better, but he’s also getting lucky.
However, the area where Tillman has really improved is when there are runners in scoring position. His walk and strikeout rates have actually gotten worse. He has a 20 K% and a 10.7 BB% in 2016 with RISP compared to 21.8% and 7.9% in 2013-2015. But he also has a HR% of 1.30% and a BABIP of .220 in 2016 compared to a HR% of 2.2% and a BABIP of .287 from 2013-2015. As a result, his OPS from 2013-2015 with RISP was .678 and his wOBA was .295 but in 2016 his OPS was .557 while his wOBA was .258.
His wOBA in play with RISP was .257 in 2016 and .344 from 2013-2015. It’s possible that his HR% indicates improvement from 2013-2015 rather than random chance. After all, his 2013-2015 home run rate suggests that he should have allowed slightly roughly 1.7 home runs instead of the 1 home run that he actually has allowed. If so, his lower HR% accounts for 40% of his improvement while the other 60% is a result of his abnormally low BABIP.
Given that his K% and BB% aren’t particularly good, it’s reasonable to expect some regression. His OPS with RISP ranks 20th out of 99 qualified pitchers, suggesting that he isn’t unique in this regard. There were other pitchers that also have been successful in these situations despite poor strikeout and walk numbers which should be expected given the small sample sizes we’re dealing with.
It does appear that Tillman has gotten lucky with pitches put into play with RISP. He’s given up slightly fewer line drives and fly balls in 2016 compared to 2013-2015 while allowing slightly more ground balls and popups. But this dataset seems to think that Tillman has given up a .892 wOBA against popups in 2016, so it seems that there isn’t a drastic change in the type of contact he’s allowing. The drastic change is that the average FB and LD in 2016 is only doing 85% of the damage that it did from 2013-2015 while the average GB is doing only 62.5%.
Likewise, it’s worth noting that Tillman is having more success throwing all of his pitches with RISP in 2016 than he has previously from 2013-2015 and that batters are doing less damage putting his pitches in play with RISP than in normal situations.
All of this seems to indicate one of two things. The first possibility is that Tillman has discovered a way to not just improve his off-speed pitches so that they are harder to hit, but also that they’re more likely to result in outs. In addition, he’s found a way to be super-efficient with RISP and will be able to maintain a .220 BABIP with RISP. If so, then this will be a strong season for him.
The second possibility is that he’s improved his command of his off-speed pitches and thus will be able to get more strikeouts but has also been fortunate with RISP. If this is the case, I would expect his results and thus his ERA to regress towards the mean. This probably does explain why his FIP is so much worse than his ERA and that his FIP probably more accurately describes his performance than ERA.
Of course, and especially after 2015, most fans would be happy with a 3.90 ERA from Tillman. This would certainly be an improvement and would make him a solid member of any rotation. He’ll provide some stability to a rotation that sorely needs it and is on pace to earning an all-star bid. But he also probably isn’t the ace that the Orioles need. The Orioles shouldn't overweight his current performance when deciding to give him an extension. It looks like he’s just back to his usual of being a solid but not great starter.