Bobby Cassevah had his first cup of coffee with the Angels in 2010, making three short stints in the bullpen at the beginning, middle and end of the season. While his 3.15 ERA (3.63 FIP) in 22 innings was nothing to scoff at, he didn’t exactly inspire thoughts of greatness. His 1.0 K/BB and team-worst 3.60 K/9 seemed to place him in the echelon of back-up mop-up guys.
Back in AAA Salt Lake for the first half of 2011, Bobby put up a rather uninspiring, albeit PCL-handicapped, 4.76 ERA (4.70 FIP) in 22.1 innings.
Despite the relatively poor numbers, a back injury to Fernando Rodney in mid-June resulted in a call-up for Cassevah. He excelled enough in his first eight appearances that when Rodney returned in late July, it was Trevor Bell packing his bags for the PCL, not Cassevah.
Remaining with the club through to the end of the season, Bobby became an unexpected asset, amassing a 2.72 ERA (3.66 FIP) in 39.2 innings.
King of Worm Burners
While some of Cassevah’s success likely came from an improved K/9 rate (5.45), much of it stems from his extreme ground ball tendencies¹.
Just how extreme? The league average ground ball rate for all pitchers in 2011 was 44.4%. When the ball was put in play off of Bobby in 2011, it resulted in a ground ball a staggering 70.3% of the time.
Among relievers with 50 or more innings pitched the last two seasons, Cassevah’s ridiculous 66.7% GB rate is third in all of baseball, and he trails only wunderkind Johnny Venters in GB/FB rate.
Though Bobby had managed to accrue grounders at a 61.3% clip in 2010, at the time I attributed it to small sample size (only 22 innings) so I thought some downward regression was in order.
Well, with GB% and GB/FB rate stabilizing at 150 and 200 batters faced, respectively, and Cassevah now at 251 major-league batters faced over the last two seasons, it looks as though his numbers have normalized. They’re just not normal.
Primarily a sinker-ball pitcher, a look into Cassevah’s minor league numbers reveals that he has always succeeded in provoking a high level of ground balls. Between AA and AAA in the 2009-2010 seasons, for instance, Cassevah averaged an incredible ground ball rate of 73%.
So, Fewer Homeruns Then?
Along with standing among the league leaders in ground ball stats the last two seasons, Cassevah is also in the thick of the HR rate leaders: his 0.15 HR/9 and 3.1% HR/FB ratio rank 2nd and 5th in the league over that timeframe.
But while Cassevah has demonstrated a penchant for not giving up home runs at the major league level thus far—just one given up in 59.2 MLB innings—expecting it to stay that way is probably unrealistic.
Despite conventional wisdom to the contrary, the ability to induce heaps of ground balls doesn’t always correlate with a low home run rate². Thus, Cassevah’s HR/FB ratio will not stay at 3.1% forever. That does not mean he’s “due” to give up a bunch of home runs this season—regression doesn’t work like that—but don’t be surprised if he at least starts to drift closer to league average in that regard.
The only thing a surplus of ground balls does definitively do in regards to home runs is give batters fewer opportunities to hit them. This also extends to extra base hits in general, as most doubles and triples result from balls hit in the air.
Pitching to Contact
It would seem to make sense (to me, at least) that keeping most hitters from squaring up the ball—whether an artificial skill or not—would coincide with a large number of whiffs.
This is not the case for Cassevah.
While Bobby has been one of the best ground ball guys in the game of late, he has had the 10th worst K/9 rate of any reliever in that same timeframe.
What’s more, of the relievers in the top 10 in GB% over the last two seasons, Cassevah is one of only two pitchers with a K/9 rate under 6.00. Surrounded on the list by high K/9 guys like Johnny Venters, Mark Rzepczynski and Brad Ziegler, Cassevah’s lone pitch-to-contact compatriot is a guy by the name of Blaine Boyer. It may not always be the case, but most of the time it’s probably not a good sign if you’ve never heard of the guy to whom you’re being compared.
So what, if anything, can Bobby do to improve his strikeout rate?
He Should be All-Right
What Bobby should do—and what hopefully our no-longer-inept front office realizes—is never pitch to a left-handed batter ever again.
Take a look at the insane platoon splits Bobby has endured in his career so far:
As striking as the over 300-point gap in OPS is, it pales in comparison to the split in his K/BB numbers. Not only does Cassevah lack the ability to strike out left-handed batters, he also manages to walk them at double the rate of righties.
An inspection of his 2011 splits³ in regards to pitch selection and location reveals that much of this may be attributed to the way he goes after (or doesn’t go after) lefties.
vs. RHB – 2011
vs. LHB – 2011
The nice, evenly distributed palette of pitches exhibited against righties is thrown into sharp relief by the massive cluster of pitches effectively situated in the other batter’s box against lefties. Cassevah doesn’t just avoid the inside corner against lefties, he seems to avoid the outside corner as well.
His reliance on the outside part of the plate—and failure to actually hit it—against lefties is the key factor in his polarized K/BB splits. Bobby throws his sinker for a strike 68.4% of the time when facing right-handed batters, largely because he uses the entire plate. With lefties, in spite of throwing his sinker significantly more, he only hits the zone 54.3% of the time.
Perhaps Bobby could find more success against lefties if he were to adjust his game plan and attack the inside corner a bit more, but it’s probably an easier adjustment to just have him face them less, if at all.
Removing lefties from the equation completely, Bobby’s numbers look excellent. His K/9 rate jumps above 6.00—nicely into the realm of the other successful ground ball relievers—and his walk rate plummets into better than average territory.
If used effectively, Bobby’s unique ground ball ability can be a huge asset to the team going forward. The key will be to use him in situations that give him the highest probability of a positive outcome.
In other words, use him as much as possible against righties, particularly in double play or sac fly situations, and avoid using him against lefties whenever possible.
 Fun fact: There are four Bobby Cassevah highlight videos on MLB.com. In those videos he faces 11 different batters. The results: eight ground balls (three double plays), two strikeouts and one random stolen base by Coco Crisp I which we never get to see what the batter did. My money is on a ground ball. …and yep, ground ball.
 HR/FB ratio for those with a proclivity for ground balls can be erratic and deceiving (see: Peter Moylan). For instance, if three of Bobby’s next five fly balls leave the park—but occur over 10 appearances—then his HR/FB ratio would be a bit misleading. It takes longer for a ground ball pitcher’s HR/FB to stabilize due to the simple fact that they allow fewer fly balls.
 PitchF/X was unaware that Bobby threw a sinker until 2011, so including 2010 data would throw things off a bit.