In April and May, Charlie "Ground Chuck" Morton used a sinker-centric approach to induce weak chopper after weak chopper. Opponents hit a collective .252, got on base at a .329 clip and slugged just .315 against Morton.
Since the calendar flipped to June, however, hitters have put Ground Chuck through the meat grinder. Morton has turned every hitter into Dustin Pedroia out there, allowing a .335/.410/.473 triple-slash over the past two months.
There doesn't seem to be much difference in the location of Morton's sinker:
But hitters are making louder contact:
To be sure, some of the drastic change in Morton's performance is due to poor luck -- he had a .286 batting average in April and May, but his BABIP since is .382. But it's also true that batters are doing more extra-base damage.
Opponents had a paltry .063 Isolated Power (slugging minus batting average) over the first two months, and a .138 ISO in June and July. That June-July ISO is right around the league average, which is a problem considering that Morton doesn't strike out many hitters and has so-so control. He needs to limit doubles, triples and homers to make up for his other shortcomings.
Perhaps with ample video and advance scouting reports on Morton's new delivery and pitching approach now available, batters have simply become more accustomed to the fact that he throws sinkers so often. Seven or eight times out of ten, a batter is going to guess right if he thinks he's going to get a low-90s pitch that tails to Morton's arm side.
Morton's best hope at turning his season around and doing something to avoid being a bunching bag to left-handed hitters (they have a .380/.458/.542 triple-slash in 2011) might be a little more variety. In particular, he has shown a promising high-70s curveball with plenty of break. Curveballs tend to have less of a platoon split than other pitches (sinkers have the largest split), and if thrown more often, the breaking ball would keep hitters from waiting for a sinker in that one spot.
Check out the pitch break and velocity of Morton's curve (blue), compared to his sinker (orange):
Hitters aren't just passive zombies at the plate -- they make adjustments based on the information at hand. The word has gotten out on Morton's sinker. Now, it's time for him to make an adjustment of his own by being less predictable on the mound.