On Friday afternoon at Wrigley Field, with the Cardinals trailing the Cubs 3-2 heading to the seventh inning, Mike Matheny called on left-handed reliever Zach Duke to replace his starting pitcher Carlos Martinez. Duke turned around Ben Zobrist to bat right-handed, inducing a fly out to left field, before snaring a weak liner back toward the mound off the bat of Anthony Rizzo. With the right-handed hitting Willson Contreras due next, Duke was relieved by right-handed throwing Matt Bowman, who promptly recorded the third out. All told, Duke threw just six pitches, three for strikes.

On its own, Duke’s appearance doesn’t appear noteworthy. Nothing spectacular happened, and Duke has pitched in a lot of games. In fact, over the past three full major-league seasons, Duke was about as likely as anyone in the league to make an appearance on the mound in a game.

Most MLB Pitcher Appearances, 2014-2016 Pitcher Games Jeurys Familia 230 Bryan Shaw 229 Zach Duke 226 Mark Melancon 225 Tony Watson 225 SOURCE: FanGraphs

So what made Duke’s appearance special? To understand that, it’s necessary to begin with the fact that this was his first appearance in an MLB game in 2017. As the regular season ended last season in early October, the Cardinals reported that Duke had undergone Tommy John surgery while also having a flexor muscle repaired in this left arm.

Tommy John surgery has become something with which all baseball fans are familiar. At this point, it’s no longer shocking to hear that a pitcher has torn a UCL in his throwing elbow. By my calculations, over 26% of pitchers who appeared in an MLB game last season have had this type of procedure.

It’s also generally accepted that most professional players who require Tommy John surgery return to play again at roughly the same level, with several studies reporting return rates in the 80% range or higher. My own Tommy John surgery database puts the return rate for all recorded professional players who had surgery in 2015 or earlier at 85%, with MLB players at 79%. In other words, it’s fairly common for an MLB pitcher to (a) undergo a UCL reconstruction surgery and then (b) return to pitch again at the MLB level.

What stands out about Duke’s return to the mound at Wrigley Field on Friday is that it occurred only 287 days from the date of his surgery*. This is a much shorter timespan than the typical pitcher requires to return to the level at which he was playing before suffering his injury. I’ve started tracking a number of different rehabilitation milestones for players recovering from Tommy John surgery, so we can compare Duke’s progress to other professional pitchers through a few snapshots.

Of the over 1,400 Tommy John surgeries on professional baseball players that exist in the database, I have what I believe are accurate surgery and return dates for 601 pitchers since the original surgery by Dr. Frank Jobe in 1974. Of those 601 pitchers, Zach Duke’s return to the same level of baseball is the ninth fastest. Former Cardinals pitcher Ken Dayley had by far the shortest return time, recovering from a surgery after the 1986 season to pitch again in MLB before the end of May in 1987!

A relevant observation from the fastest returns above is that nearly all of those who recovered to pitch quicker than Duke — including every MLB pitcher — had their surgeries more than a decade ago. If we restrict our pool for comparison to the last decade, the brevity of Duke’s absence looks even more remarkable.

Fastest Return to Same Level of Baseball for Pitchers

After Tommy John Surgery, Surgeries 2006-2016 Player TJ Surgery Date Team Level Age Return Date (same level) Recovery Time (Days) Casey Crosby 11/27/2007 DET HS 18 8/15/2008 262 Zach Duke 10/7/2016 STL MLB 33 7/21/2017 287 Josh Mueller 9/11/2013 COL AA 24 6/30/2014 292 Parker Frazier 9/22/2009 COL A 20 7/23/2010 304 Lucas Giolito 8/31/2012 WAS Rk 17 7/3/2013 306 Duane Below 6/5/2009 DET AA 23 4/10/2010 309 Gabe Speier 9/1/2013 BOS Rk 18 7/10/2014 312 Charlie Furbush 6/1/2008 DET A 22 4/11/2009 314 Taylor Jordan 9/7/2011 WAS A 22 7/20/2012 317 Jose Contreras 6/20/2012 PHI MLB 40 5/5/2013 319 SOURCE: Tommy John Surgery Database

Of the 468 qualifying Tommy John surgeries over the past decade, Zach Duke’s return was the second fastest of all professional pitchers — and the fastest by a full month of the 157 pitchers who had the surgery while pitching in MLB. Jose Contreras returned to make seven MLB appearances in his age-41 season in 2013 before moving on to the Mexican League, where he was pitching even last season at age 44!

On this list, we see three organizations (Colorado, Detroit, and Washington) with multiple players who’ve returned much quicker than the average pitcher, perhaps suggesting they have had a more aggressive (or at least different) approach to rehabilitation from Tommy John surgery than most other organizations for pitchers in their minor-league system. The most interesting name to appear on the quick-to-return list outside of Duke is Lucas Giolito, the highly touted prospect whose stock has fallen as his velocity disappeared, but who still tantalizes talent evaluators with his potential.

Another metric that I’ve begun to track is the time between Tommy John surgery and a pitcher’s first professional game at any level — that is, for example, when an MLB pitcher first appears in a minor-league game to start his rehab assignment. For Duke, this came on June 30th for the Cardinals’ Gulf Coast League affiliate.

Duke soars to the top of this list of the 85 pitchers whose returns to the professional game I’ve tracked. The only other pitcher who appeared within two months of Duke is teammate Lance Lynn, who underwent Tommy John surgery the offseason prior. Lynn was also on an aggressive return schedule, but in his case ended up shutting down his season at the end of August to prepare for a healthy 2017 return. Before examining the Cardinals in more detail, consider Duke compared to his peers for one final rehab milestone.

These are all of the pitchers for whom I have data regarding the first time they threw off a mound during their rehabilitation from Tommy John surgery. Of course, this type of data — which I’ve culled from various media reports — is a little less precise than actual game data that’s recorded by multiple websites.

Even with that limitation established, however, this final table reveals how quickly Duke returned relative to other professional pitchers. Nearly everyone else on this list is an MLB pitcher, and we see first throws off a mound clustering around 10 and 11 months after surgery. Duke came in at just over six months. This sort of timeline is closer to when pitchers often begin a throwing program of any sort. Nathan Eovaldi and Greg Holland both took over 180 days from their surgery dates before they began to throw at all, never mind throwing off of a mound.

Since the high concentration of Tommy John surgeries that occurred around 2012, organizations have generally become more conservative with pitchers in their return times from the procedure. The more conservative approach has also been attributed to a better understanding of how long it takes for the graft within the elbow to heal.

That said, with all else being equal, a faster return from Tommy John surgery back to where a pitcher left off prior to surgery is obviously desirable. The key is that players must be able to perform at an appropriate level and to stay healthy upon their return. Recent quotes from both Matheny and Duke highlight some key aspects of Duke’s rehabilitation process.

“Just hats off to Zach and how he’s worked and also to our medical team and how they’ve continued to be open-minded and use all the information that they have to push guys forward,” manager Mike Matheny said. “There are a lot of positives that we’re hearing. I would love to be able to throw him into the mix.” “It’s been almost scary good how well it’s gone,” Duke said. “No setbacks at all, so I’m just kind of really thankful right now. Hopefully these last few days, next week or so, can continue that.”

These comments suggest to me that the Cardinals’ medical staff is pushing athletes to recover more aggressively than is usual — and likely using a data-driven approach such that, if a player’s body responds at each given stage, they continue pushing forward toward a faster recovery period. Recent popular examples of an expedited return from surgery fueled by a data-driven feedback loop include Marcus Stroman’s return from knee surgery and Troy Rallings’ return from Tommy John surgery.

While the known sample size of recoveries that are highly data driven rather than formulaic in their adherence to a standard rehabilitation schedule is too small to access, in my opinion this is a much smarter way to approach return from major surgery in this time and age. Every surgery is a little different, and every athlete is unique, so being conservative across the board with all pitchers may result in unnecessarily missing out on an earlier contribution from a subset of those pitchers.

It would have been very easy for the Cardinals to have defaulted to a more conservative, league-average pace for Duke’s return — especially given the time of year that his surgery occurred. Instead, they involved him heavily in team activities right from spring training, and by allowing Duke to blow through milestones unimpeded without any sign of setbacks, it has provided them with a much needed bullpen arm for the second half of their 2017 season.

*One qualification to make about Duke’s surgery is that I have treated it as an actual Tommy John surgery, since it was reported as such by multiple media outlets at the time of the procedure and has been confirmed as such by Cardinals GM John Mozeliak.

The fact that Duke plays for the Cardinals in particular made this assertion somewhat less concrete in my mind than had he played for any other organization, given that Cardinals team doctor Dr. George Paletta has performed UCL InternalBrace repair surgeries in lieu of Tommy John surgeries on at least three Cardinals players (Mitch Harris, Seth Maness, and Jordan Schafer). This alternate surgery, first developed by Dr. Jeffrey Dugas at the Andrews Sports Medicine & Orthopedic Center in Birmingham, Ala., carries with it the potential for a shorter recovery time than with a traditional Tommy John UCL reconstruction surgery.

Duke’s surgery was attributed to Dr. James Andrews. To this date, all reports of Duke’s surgery suggest it was an actual Tommy John surgery (in addition to a flexor muscle repair).