Starting Pitcher Swinging Strike Rate Surgers

A week ago, I identified the starting pitchers whose xK% marks were most above their actual strikeout rates. The swinging strike component is the most significant in my xK% equation, so let’s take a look at which pitchers have enjoyed the biggest surge in their S/Str (Baseball-Reference metric) this season. The 2015 numbers do not include yesterday’s starts.

First, some background:

S/Str = strikes swinging (without contact) / total strikes; so the percentage of strikes that are of the swing and miss variety
SwStk% (from FG) = strikes swinging (without contact) / total pitches; so the percentage of pitches that are of the swing and miss variety

The difference between the two metrics is the denominator — the Baseball-Reference rate is only out of strikes, while the FanGraphs rate is out of all pitches.

2015 league average S/Str = 16.2%
2014 league leading S/Str = 24.2% (Francisco Liriano)

The top dogs are typically in the low-20% range.

Woah, James Shields. His velocity is relatively stable and he’s throwing his curve slightly more at the expense of his cutter. But his pitch mix is generally in line with previous seasons. So what’s behind the surge? His four-seam and two-seam fastballs, along with his cutter have all seen their SwStk% marks double from last season, his signature changeup has induced even more whiffs than he already had and his curve has also induced more swings and misses. So, literally every single pitch of his has been significantly better. We knew that all else being equal, he would enjoy a strikeout rate spike upon his move to the National League. But certainly not to a mark above 30%! I was rather bearish on him this year. Oops, I think I’m going to be wrong.

Danny Salazar is now throwing a curve ball. And it looks like this. Salazar already has a great fastball, a ridiculous changeup and respectable slider. Hitters may now choose to simply quit before even entering the batter’s box. But somehow despite his outwardly awesome stuff, his career line drive rate is well inflated at 24.9%. It’s led to a high .333 career BABIP, though I’m sure the poor Indians defense also has something to do with that. If his luck ever neutralizes, he could quickly become one of the best pitchers in the American League.

Jimmy Nelson was a popular preseason sleeper, though the concern was he was just a two-pitch pitcher, featuring the fastball and slider. He has added a curve this year and it’s been pretty darn good, while his slider has been fantastic as well. But, it’s doubtful that his sinker is going to sustain a 9% SwStk%, as the league average is around 5.4%. So although I think his current S/Stk mark is going to decline, the addition of the curve to neutralize lefties could very well result in that breakout year.

Obviously after turning from my favorite person in the world to thinking he is overvalued, Andrew Cashner is finally striking out batters at a rate we all expected from him two seasons ago. It’s all in that slider, as its SwStk% has jumped above 20%. he has also gotten back to his 2013 mix of four-seam vs two-seam fastballs, and the four-seam generates more swinging strikes than does the two-seamer. But the tradeoff is a higher fly ball rate. Once his line drive rate gets back to normal, that might take away grounders. Since I’m not sure that big jump in slider SwStk% is sustainable and the 10% mark from his two-seam fastball certainly isn’t, this S/Stk rate is almost certainly going to decline. But, he looks like a good bet to maintain a 20%+ strikeout rate all year…finally.

The difference for Chris Archer? Throw the slider even more! Clearly, he’s not concerned about blowing out his elbow. But the Rays may want to have Dr. James Andrews on speed dial. Archer threw about 29% sliders last year and 33% in 2013, but is at a whopping 39% this season. The slider increase has come at the expense of his fastball, which is exactly why he’s inducing so many more swings and misses. His strike percentage is up as well, so the strategy is working. And the slider’s SwStk% is at a career best above 20%, while his infrequently thrown changeup is inducing swinging strikes significantly more often as well. Seems like a slightly risky strategy, but single-season leaguers might as well enjoy all those sliders for as long as he keeps slinging them so frequently.

Joe Kelly has transformed into a completely new pitcher, which is an article in itself. It’s pretty clear what’s going on here. His fastball velocity, which was already high, has jumped another tick, averaging 96 mph. He still throws it a lot though, which is most likely holding his S/Str back from potentially being even higher. He is also throwing his slider more often, essentially instead of his curve ball. He has nearly scrapped his changeup and has thrown more four-seamers, decreasing the usage of his two-seamer. The two-seamer has been terrible at inducing swinging strikes, while the slider has already been much more effective than his curve. The change in pitch mix, plus bump in velocity, all perfectly explain his increased rate of swings and misses. They have robbed him of his high ground ball rate though, but this version is more appealing to fantasy owners. Now if only he could get his HR/FB rate down and start stranding runners!

So I guess that poor Scott Kazmir second half wasn’t a predictor of disaster after all, eh? His velocity hasn’t moved, but he has slightly altered his pitch mix, throwing his cutter more often at the expense of both his slider and curve ball. His changeup has been better than ever, while his two-seamer is getting swinging strikes at the highest rate of his career. I’m not confident that will continue, but his performance just confirms that last year’s second half truly was nothing to worry about.