22 June 2015

Why Chris Tillman Has Struggled in 2015: Part I

(This series of posts include data up until 6/20)

Chris Tillman was considered the Orioles’ ace going into this season. Nate wrote an article where he argued that Chris Tillman was at least a good pitcher. But Tillman has struggled so far this year with a 5-7 record, an ERA of 5.58, an FIP of 4.80, an average of only 5.46 innings per start and a value of .4 fWAR. These numbers are disappointing and it makes one wonder what exactly happened. More to the point, it makes one wonder whether he's just having bad luck so far or whether this is something more serious.

A closer look at Tillman's performance shows where he's struggling as shown below in the chart (click to enlarge).



Tillman is struggling when the bases are empty primarily because he’s walking nearly 17% of batters when the bases are empty as opposed to his 2013/2014 norm of roughly 7 to 8%. In 2013 and 2014, Tillman threw roughly 37% of his pitches with the bases empty for balls in the past two years but this year that rate has jumped to 42%. This partly explains why (although his BABIP of .327 and double rate of 7.8% certainly don’t help) opposing batters have a wOBA of .395 against him when the bases are empty and why he has a bases empty FIP of 6.01. Historically, Tillman has had an FIP in the low to mid 4s with opposing batters putting up a wOBA in the low .300s.

To put this in the proper perspective, suppose that Tillman only gave up 11 walks to 139 total batters faced for a 7.91 BB% instead of giving up 26 walks to 154 total batters faced for a 16.88 BB%? While this methodology is overly simplistic it will be roughly accurate and implies that Tillman would have a WHIP of 1.56, a wOBA of .326 and an FIP of 4.54. This is reasonably similar to his performance in 2013 and suggests that his performance with the bases empty would be acceptable this year if he gave up walks at his normal rate.

Tillman has been effective this year with runners on base or in scoring position. Opposing batters are averaging a .312 wOBA with runners on base and a .278 wOBA with runners in scoring position, which is reasonably similar to his performance in 2013 and 2014. Likewise, Tillman’s FIP of 3.87 with runners on base and 3.34 with runners in scoring position in 2015 is similar to his performance in 2013 and 2014. He isn’t having any problems throwing strikes with men on base this year either. All and all, he’s been effective when runners have been on base.

There's a problem with this analysis. Tillman's extra 15 walks should have cost him about 6 runs. The problem is that he's given up 45 runs so far this season in 71 innings. If he gave up 39 runs, then his ERA would be at 4.94 which is an improvement but still not very good. What other reasons could make him struggle so much?

The following chart shows how many chances opposing batters have had to hit against him in the following base states in both 2012 to 2014 and 2015. It also shows how many runners scored in each position as well as the percent of situations that Tillman was in that base state in each of those year groups and the percent of runners scoring (runners scored/chances). It does not take into account base runners that score after Tillman left the game.


This chart shows that Tillman has done better than average when only one runner was on base, but that he's done poorly this year with multiple runners on base despite the fact that his on base FIP and wOBA have been remarkably similar in 2012-2014 and 2015. This has cost Tillman an extra six runs and I'm inclined to chalk it up to bad luck. It seems unfortunate that in the thirty-three chances that opposing batters have had a chance to bat with multiple runners on base that they've scored about eleven more runs than should be expected or roughly twice as many.

In addition, Tillman has the twelfth worst LOB% in the majors this year (out of 104). Two of the Orioles starters (Miguel Gonzalez and Wei-Yin Chen) are in the top ten in that stat while Jimenez is ranked 31st and Norris hasn't pitched enough innings to qualify. This further supports the argument that Tillman probably has had some bad luck with multiple men on base and that we should expect improvement.

All in all, it appears reasonable to conclude that Tillman has struggled this year because he's thrown too many balls and given up a lot of walks, that he's done surprisingly well with one runner on base, but has struggled with multiple runners on base and because he has a higher BABIP with no runners on base than one should have expected. This has forced Tillman to face more batters this year with someone on base than he has with no one on base and thus given offenses plenty of chances to bat with a runner on base. Offenses are simply too good for pitchers to be successful if continuously spotted base runners and unsurprisingly have taken advantage. If Tillman wants to improve he needs to find a way to pitch effectively with the bases empty by primarily throwing more strikes and thus avoiding walks.

This post gave a basic explanation as to why Tillman has struggled this year. In the next part of this discussion, I intend to look at specific pitches and see whether he is struggling with a specific pitch.

3 comments:

James Sass said...
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James Sass said...

Fantastic analysis Matt, Hopefully Tillman can decrease his walks.

Matt Perez said...

Thanks James. I'm glad you enjoyed it and I hope you like the other parts also.