Mike Matheny is the manager of the St. Louis Cardinals, the team that brought in the then 37-year old Randy Choate in the offseason before 2013. Choate was signed to a 3-year deal worth $7.5M. It was back-loaded ($1.5M, $3M, $3M), probably to ensure that Choate would get as little money as possible from the Cardinals if he chose to retire before the contract was finished.
Randy Choate was definitely seen as a LOOGY (Left-handed One Out GuY) - or basically a left-handed reliever whose best role is getting out the toughest left-handed batters the team will face in the most dangerous late-game situations. Coming to the Cardinals, Choate had faced 1,344 batters. 755 of them (or 56.18% of them) had been left-handed batters. He had given up an OPS against vs. RHB of approximately .800 while only allowing an OPS against vs. LHB of approximately .540 at the time of his signing. He was MUCH better against those tough lefties than basically ANY righty.
Because of this, Randy Choate's usage through the 2012 season had him enter 476 career games, while pitching only 309 1/3 innings in that time. That means, he averaged getting 1.95 people out per appearance. That isn't to say he was bad - as it seems on the surface - it's just his role. For the record, he only allowed 1.338 baserunners per 9 innings in that time.
On Mike Matheny's 2013 NL Pennant winning team, Choate was used incredibly well as a LOOGY. First of all, he pitched in 64 games and only threw 35 1/3 innings in 2013. He faced 141 batters, with 70.21% of them (99) being lefties. He did much better than he normally had in his career, keeping the 42 RHB he faced to a quite low .635 OPS and the lefties all the way down at a .492 OPS!
In 2014, the Cardinals decided (publicly) that they needed more innings out of Choate in the bullpen. Why? Nobody is exactly sure. They allowed Choate to face 40.54% RHB in 2014 and he gave up a .938 OPS to those righties while holding lefties to an even smaller .351 OPS against. He ended up facing 88 lefties and 60 righties last year, for 148 total batters.
In 2015, Mike Matheny has swung to the EXTREME using Choate as LOOGY-ish as humanly possible thus far in the season. Through 60 team games, Choate has entered 27 of them and pitched only 11 innings and to just 44 batters - 37 of them left handed (84.09%!!!!). In fact, out of the 27 games in which Choate has entered, he has exited after throwing to just one batter in 22 of them - or 81.5% of the time. He has thrown just 72 pitches in those 22 games, mostly retiring hitters after just 3.27 pitches per plate appearance.
There have only been 3 times this year in which Choate has thrown either 2 or 3 outs. In those 3 outings, he has recorded 8 outs on just 9 batters faced and 27 pitches. He has also been asked to "bite the bullet" twice this year, facing 6 batters to get 4 outs in a 6-run win over the Phillies in late April and to record 5 outs on 7 batters on 28 pitches against Cleveland in a 2-run loss in mid-May.
While not quite as effective by OPS against in 2015, it is still overall a respectable .629 and with all the lefties he's been facing, could end up being even better than that (at age 39 no less) if Matheny continues in his evolution using this LOOGY.