Stephen Strasburg started two days ago, but I wanted to get this out there. Strasburg has added a slider to his repertoire, to give him another weapon against left-handed batters. He threw the pitch three times in two innings in his Tuesday start, saying "I wanted it to look as much like a fastball as possible, so if I get a little bit of movement, that's all I'm really looking for. I'm not going to dump my other offspeed pitches for it. It's just going to be something to keep them from cheating to the fastball as much."
Strasburg's main offspeed pitch against left-handers has been his curveball ... and it's been an effective pitch for him. Left-handed batters hit just .113 against it (6-for-53) with 32 strikeouts in 56 plate appearances. In fact, as Justin Havens of ESPN Stats & Information pointed out, Strasburg was pretty effective overall against left-handed batters in 2013:
Opponents' batting average: .218 (sixth-best among 57 qualified right-handed starters)
Opponents' OPS: .629 (fifth)
Well-hit average: .101 (first)
Swing-and-miss pct.: 45.6 (25th)
Chase pct.: 28.8 (21st)
As the numbers suggest, Strasburg was good at inducing weak contact but only middle-of-the-pack in generating misses. Why? Left-handers seem to have little trouble picking up his fastball. They hit .254/.351/.415 against it in 2013, but with 28 walks and just 23 strikeouts in 223 plate appearances. The curveball and changeup are effective when Strasburg gets ahead in the count but lefty hitters can still attack the fastball. Thus, the development of the slider and Strasburg's hope that it resembles his fastball.
The bonus if the pitch develops into a weapon: Strasburg could be even more devastating against right-handed batters, since a good slider is a wipeout pitch against same-side hitters. Righties hit .197/.258/.294 against Strasburg in 2013; that was the fifth-lowest batting average allowed and seventh-lowest OPS for those righty-versus-righty matchups among starting pitchers.
Strasburg posted a 3.00 ERA in 2013 in 183 innings. It seems odd to say about a guy who has one of the fastest fastballs in the league, but throwing his fastball a little less often may actually be a good thing. I'm thinking this is the year that ERA dips well below 3.00, the innings top 200 and Strasburg gets into that Cy Young mix.