The title of this article pretty much sums up what we’re going to be looking at. I took the top ten qualified starters in K% from 2014 and 2015, and looked at any significant changes in rate between those two years.

There are four starters who were either in the top ten last year or this year who have seen at least a 5% change (increase or decrease) in their K%. Has anything changed about these pitchers’ velocity, approach, or control that has led to these changes?

1. Chris Archer 21.1 K% in 2014 to 30.7 K% in 2015

Archer has experienced one of the more significant spikes in K% of starters in the top ten this season. A look at how often he has used particular pitches shows some significant changes that he has made this season. Toward the end of 2014, he was using his slider only about 25% of the time, but in 2015 he’s throwing that pitch 38.1%. His rise in slider rate has largely come from throwing his sinker a lot less. Hitters are swinging and missing on his slider more than 20% of the time, and it has become an incredibly devastating pitch.

Owen Watson of Fangraphs noticed this change in approach at the end of April, and he gives more details regarding how Archer is using the slider this season. Of particular note Watson writes, “He’s now using his slider more in all counts and situations, but the biggest change is a 25% jump in two strike usage to left-handed hitters from 2014 to 2015. It’s now become his go-to out pitch against lefties — he’s currently throwing it 59% of the time to left-handers with two strikes. In those situations, batters are 0-14 so far this season with nine strikeouts.”

2. Danny Salazar: 25.3 K% in 2014 to 32.2 K% in 2015

Salazar has had two noticeable changes in his pitch repertoire this season. In 2015 he’s started to throw a curveball (6.4%) that was virtually non-existent prior to this season. He’s also throwing a splitter more than 20% of the time that has largely resulted in a drop in four-seam fastball use.

His splitter has been particularly effective in terms of swings and misses. In April, hitters swung and missed at 36.92% of Salazar’s splitters, and in May that percentage has stayed above 20% (23.13). In 2013, Carson Cistulli wrote about how devastating Salazar’s splitter (split-change) is, and it looks like he’s only gotten more comfortable throwing that pitch as he’s matured.

3. Stephen Strasburg: 27.9 K% in 2014 to 21.2 K% in 2015

One of the more significant drops in K% for pitchers who were in the top ten one of the past two seasons is Stephen Strasburg. Strasburg hasn’t experienced a significant dip in velocity, and he’s largely throwing the same pitches that he has previously in his career. What is surprising is that hitters are swinging and missing less on all of Strasburg’s pitch types.

Most noticeable is the change in swing and miss rate on his change up. In 2014, hitters swung and missed on more than 20% of Strasburg’s changeups every month (except October). However, in 2015 hitters missed on only 16.67% in April, and in May (yes it’s a small sample size) hitters have missed on just 7.69%. From 2014 to 2015 the amount he’s thrown this pitch hasn’t significantly changed. Also, the vertical and horizontal location of this pitch has not changed substantially.

4. James Shields: 19.2% in 2014 to 31.5 in 2015

Shields is experiencing quite the bump in K% from a year ago, and his pitch selection has changed quite a bit from those two years. In 2014 Shields threw his curve around 10% of the time most months. In April of 2015, however, he used it 17.53% and in May that usage has jumped to 30.86%. This increased use of his curve has come at the expense of his cutter and sinker.

Both Shields’ change and curve are generating swings and misses more than 20% of the time. It appears Shields has exchanged the use of two pitches that resulted in only a 10.6% whiff rate in 2014 (cutter/sinker) for more strikeout-friendly pitches in 2015. His curve/change combination this year is resulting in a whiff rate of 24.7%. Shields has noticeably changed his pitch usage this season, resulting in a much higher K%.

Many other authors can go into greater detail on what has changed about these pitchers. I simply wanted to write an introductory post to see if there are any obvious reasons that can account for the changes that we are seeing. I’m fairly new to using this type of data so please comment, correct, and discuss this data in the comments section.