For a non-closer relief pitcher, Kevin Siegrist was incredibly valuable to the St. Louis Cardinals in 2015. Siegrist's 1.3 fWAR cracked the top 25 of all MLB relievers and placed second on the Cardinals behind only the 2.0 posted by All-Star closer Trevor Rosenthal. Considering the last game pitched by projected set-up man Jordan Walden was way back on April 29th, Siegrist heavily rode the role of primary set-up man for nearly the entire season, appearing in an MLB-leading 81 games.
Frankly, despite being a pitcher of the left-handed variety, a role that is generally neutral in regards to batter handedness (i.e. set-up man) likely fits Siegrist best. Back in August, former editor Nick Lampe (congratulations on the Yankees internship!) touched on the topic of reverse splits a little bit, but I intend on taking an even closer look here.
Across the board, the left-handed Siegrist was better against right-handed batters in 2015, and it really was not even close. While the drastic difference may be in part due to the unpredictability of relief pitchers, I propose that the root of the issue, going forward especially, will be the change (pardon the pun) in his repertoire introduced last season.
While the changeup was a highly effective pitch for Siegrist in 2015, he rarely threw it to lefties (in fact, he threw only five to LHBs all year), and with good reason, as a lefty changeup's natural movement often falls into the wheelhouse of many left-handed batters. Plus, even before the introduction of the changeup in 2015, Siegrist was considerably better against right-handed batters, as seen in the table below:
Siegrist's career splits suggest that, going forward, he will not be as bad against lefties as he was in 2015, but at the same time, he will not be as good against righties, either. With the uncertainty of the Walden's shoulder health, I would expect Siegrist to start 2016 as the team's primary set-up man. In an ideal world, Siegrist would be saved for one of the game's most high leverage situations, but I think it has become pretty clear how most MLB managers use their bullpens.
So, why does Siegrist's complicated stat line have any effect on the role of Tyler Lyons? Well, with the expiration of Randy Choate's three-year contract a few months ago, Siegrist and Lyons (who is out of options) project to be the bullpen's two left-handed relievers at the start of the season. I would expect to see Dean Kiekhefer in stints as well, but considering his roster status is much more flexible than Lyons at this point, he will likely be riding the "Memphis-to-St. Louis shuttle" throughout 2016.
While Siegrist appears to have the "sexier" repertoire with his ability to light up the radar gun, both tables above show that he has not yet been consistently effective against left-handed batters. With the division projected to be just as competitive as it was in 2015 (with the Cardinals likely trailing the Cubs at this point), it is supremely important to have a trusty reliever that manager Mike Matheny can use against dangerous lefties like Anthony Rizzo, Joey Votto, and Jason Heyward.
On the surface, Lyons appears to be that guy. Sure, he has only faced 161 left-handed batters in his MLB career, but he has experienced success thus far (and his repertoire suggests continued success as well):
The only question that remains is if Rizzo is up in the top of the eighth inning of a one-run game, will the Cardinals manager turn to a pitcher who has displayed success against left-handed batters (Lyons) or will he go with his guy who is generally reserved for the eighth inning (Siegrist)? Now, if the choice is Siegrist, please, for the love of the game (remember, a game in April counts the same as a game in September), waste a pitch in an 0-2 count: