Kris Medlen vs. the St. Louis Cardinals: Battle of the Grounder

On Friday, the St. Louis Cardinals travel to Turner Field to face the Atlanta Braves in the inaugural National League Wild Card play-in game. The Braves have named youngster Kris Medlen as their starter in this sudden death match-up, a pitcher not many folks outside of Braves fans had heard much about before the second half of this season. Heading into the most important game of the season, let's take a look at the starting pitcher Atlanta has pinned its NLDS hopes on.

Medlen is a 26 year old righthander who has spent parts of four seasons in the big leagues. He has come out of the bullpen and been a starter. In 2009, he made 37 appearances for Atlanta, 33 of those as a reliever. The following season, Medlen made 14 starts and 17 relief appearances. Last year, he made two relief appearances that totaled 1 2/3 innings. Medlen started the 2012 season in the Braves bullpen and made 38 appearances in relief before being shifted to the starting rotation, where he has been dominant over 12 starts.

Here is a chart comparing Medlen's stats coming out of the bullpen to those as a starter over the course of his big-league career. Interestingly, his career numbers in relief are quite similar to his career numbers while starting. Medlen has been effective in both roles.

The reason Medlen is starting this must-win game for the Braves is not his career performance as a starter, but his 2012 performance as a member of the Atlanta rotation. Medlen was good in relief for the Braves in the first part of the season. Since moving to the rotation, he's been excellent. Here is a chart comparing his 2012 stats in relief to those in the rotation.

Usually, a pitcher will see his strikeout rates fall and his walk rates rise when moving from relief to starting. For Medlen in 2012, the opposite has been true, and in dramatic fashion. Medlen has halved his walk rate since moving from the bullpen to the rotation and increased his strikeout rate by 10 percent. He has also had an incredibly high LOB% and increased his groundball rate.

For whatever reason, Medlen has been in a groove while starting. It's a groove that is unsustainable. The only question is when regression will hit the young righty: Will it happen on Friday, in the NLDS, or next season?

Medlen's 2.22 FIP over 83 2/3 innings is incredibly low and probably unsustainably so. The pitchers with the five lowest FIPs in MLB this season are Gio Gonzalez (2.82), Felix Hernandez (2.84), Clayton Kershaw (2.89), Justin Verlander (2.94), and David Price (3.05). Simply put, it's unrealistic to expect Medlen to maintain a FIP that is sixty points lower than that of Gio Gonzalez.

By xFIP, the story is the same. There's no reason to expect Medlen's 2.50 xFIP to continue, given that the five lowest xFIPs in MLB are Cliff Lee (3.06), David Price (3.12), CC Sabathia (3.20), Felix Hernandez (3.20), and Zack Greinke (3.22). Medlen won't continue to put up an xFIP 56 points lower than the best xFIP in MLB.

In addition to an unsustainably great performance, some luck is afoot. The timing of Medlen's hits allowed fuels his unsustainably high LOB%. Stranding runners at a rate over 90 percent is as impressive as it is unsustainable. Jeremy Hellickson has the highest LOB% in the majors for 2012, and it sits at 82.73 percent. Only four starters have a LOB% of 80 or higher this season. At some point, the ducks on the pond are going to come home and cross the plate. It's just a matter of when.

This is not to say that Medlen is not a good pitcher. He's a very good pitcher. Medlen is just not this great a pitcher. His 2012 numbers over 12 starts are at a level similar to Pedro Martinez in his prime. As good as Medlen is, he's no Pedro.

A big reason behind Medlen's success as a starter is his repertoire. The righty relies primarily on an impressive two-seam fastball while mixing in a four-seamer, curve, and change for prime effectiveness. Via Texas Leaguers, here's a look at how he has deployed his pitches since moving to the rotation on July 31.

Not surprisingly, Medlen throws his two-seamer early in counts. He deploys it 60 percent of the time on the first pitch to a batter. Like Chris Carpenter, Medlen also relies on the groundball-inducer when behind in the count (60% vs. RHB, 58% vs. LHB). Medlen's hope is to induce the grounder, and he's adept at it. His 54.7 percent groundball rate

When Medlen works ahead of lefthanded batsmen, he uses his changeup a plurality of time, though he will drop a curve in there. Against righthanders, his pitch of choice when ahead in the count is two pitches: his curve and change. Medlen throws each about 20 percent of the time when ahead against righties. Both pitches are quite effective at inducing swings-and-misses, but his changeup is elite. Batters have whiffed on it 25.9 percent of the time in 2012 and 31.5 percent of the time since Medlen's move to the rotation. Medlen is adept at deploying his offspeed pitches when ahead in the count. Because of this, he has been able to notch strikeouts at a healthy rate of 27.2% as a starter, while allowing an extremely low number of walks. Even with Medlen's strikeout-inducing ability, the Cardinals vs. Medlen match-up will likely be won early in the count on sinkers.

As noted above, Medlen relies heavily on his sinker on the first pitch of a plate appearance and when behind in the count. Medlen throws the pitch not to generate swings-and-misses, but to generate grounders. He's be a great fit with former Cardinals pitching coach Dave Duncan. Medlen's whiff rate with the sinker is a mere 3.32 percent. When batters swing at it, they put it in play. Because of this, he has a high groundball rate. This is something that is typically good for a pitcher. Against the Cards, however, a grounder has not been nearly as positive an outcome as against the league as a whole.

In early September, Jeff Sullivan wrote about this phenomenon at Fangraphs. St. Louis was head and shoulders above the league average as well as second place in batting average on groundballs. As the season has come to a close, the Cards continue to be uncannily effective on grounders.

On grounders in 2012, the NL hit for a .239 average. The Cardinals hit for a .278 average on grounders for the season. This average on groundballs is a full 39 points above the NL as a whole. As Sullivan demonstrates in his post, there is nothing glaringly out of whack about the classifications for Cards hitters. The club has simply hit for an extremely high average on grounders this season. Here is a chart comparing the batting averages on groundballs of Friday's likely Cardinals starters to the NL average on grounders.

The Cards' success on grounders is uncanny. We probably shouldn't expect it to continue at this level, just as we shouldn't expect Medlen's performance to continue at a late-1990s Pedro level. That Medlen's bread-and-butter pitch is a groundball-inducing sinker and the Cardinals have fared so well on the grounder in 2012 makes for an intriguing Wild Card face-off on Friday. It will be a battle of the grounder. Somewhere Dave Duncan is smiling.