Nate Robertson has pitched well this spring as he tries to reclaim a role in the Tigers' rotation. Will it last? Who knows? His slider is reportedly snapping. In 14.2 IP, Robertson has allowed 13 hits and 6 walks while striking out 14. The whiffs are encouraging.
In 2006, Robertson went 13-13 with a 3.84 ERA. He's never reached that level again. His K/BB ratio has dropped and his BABIP the last two years has been right around .343. His groundball and popup rates have also suffered. He has struggled with injuries (back, elbow, groin).
Now, back to the slider. Robertson threw his slider 23% of the time in 2006. The last two years he threw his slider 25% and 27.5% of the time. Meanwhile, the velocity on his fastball dropped from 89.7 mph to 87.8 mph. So Robertson either fell in love with his slider or lost faith in his fastball, or both. And given his trouble throwing strikes, hitters were probably teeing off on fat fastballs or sliders that didn't move.
It will be interesting to track Robertson's fastball/slider this season, if he gets the chance to return to the rotation.