Mariano Rivera Lite

This shouldn't come as a monumental surprise, but at the end of the season, longtime Yankees reliever Mariano Rivera will retire from baseball. Rivera has had a storied career that includes numerous records, accolades, and little to no critics. He has miraculously yet skillfully plodded through batter after batter, sending most back to the dugout all the while throwing but one pitch. Rivera has said his cutter is a gift from God, but more amazing than the pitch is the effectiveness with which Rivera has and continues to throw said pitch.

Since PITCHf/x data became available in 2007, Rivera has thrown more cutters than any other relief pitcher, and more than all but four starting pitchers. He has the 2^nd lowest TAv against the cutter than any other relief pitcher with at least 200 at bats during which the pitcher threw at least one cutter at .190, behind only Kenley Jansen (.189). This data does not include the many years prior to 2007 during which Rivera put up even better all-around statistics, suggesting that the cutter could and probably was even better prior to 2007.

Rivera will continue to hurl cutters towards the plate until the Yankees have no more games left to play in 2013, but even though he won't be throwing cutters for the Bronx Bombers in the future, another Yankees reliever will. David Robertson, the heir apparent to the closer role in the Yankees bullpen of the future, has taken up the cutter and it would seem imprudent of him to let it go. This season, Robertson has put up some stellar relief numbers. He has a 1.68 ERA and 2.53 FIP to go along with a 1.4 fWAR, tied for 14^th amongst all MLB relievers. Since 2008, Robertson ranks in the top 10 of all relievers in fWAR, at just over 7 wins.

David Robertson is a fine reliever, but even if the Yankees choose to fit Robertson into the closer role in 2014, he will not become Mariano Rivera. Robertson's use and effectiveness with the cutter shows some similarities to Rivera, but the two men are fundamentally different pitchers in that Rivera throws his cutter in such a way to induce more contact overall than Robertson. Rivera holds a career ground ball percentage over 52%, while Robertson does his damage via the strikeout. Robertson's ability to strikeout opposing hitters often goes under the radar with flamethrowers like Craig Kimbrel and Aroldis Chapman garnering most of the attention, but Robertson has never posted a season with a K/9 under 10.00, and holds a career K% of 31.4%.

If Robertson has one flaw it is his propensity to give up home runs. In every season of his career other than 2011, Robertson has finished the year with a HR/FB% of 8.8% or higher. Like many other Yankees pitchers, Robertson's home/road splits show that the majority of the damage done against him via the home run comes at home. He sports a career HR/FB% at home of almost 10% with that number closer to 7% on the road. This season, Robertson has allowed no home runs on the road, with all four coming at Yankees Stadium. He has had some troubles with walks in the past, but he seems to have stabilized that wildness, lowering his BB% from between 12 and 13 percent to under 8 percent over the his last 110+ innings.

So, what is to come of the Yankees back end of the bullpen in 2014? Robertson seems likely to slip into the closer role, with young arms like Preston Claiborne and Adam Warren continuing to improve, and both Boone Logan and Joba Chamberlain set to become free agents, the Yankees have some decisions to make regarding their bullpen. More importantly, Robertson is set to become a free agent in 2015, meaning that next year could be his final season in the Bronx. Relief pitcher success rates seem to vary greatly in comparison to more substantial MLB players, meaning that there's a solid chance the Yankees could scrap almost their entire 2013 bullpen, build a new one, and produce similar effective results. Given the fact that all teams, including those more progressively thinking teams, want proven closers, and the fact that very few of them will be free agents this coming offseason, the Yankees best choice at the moment seems to be to make Robertson their next 9^th inning man.

Robertson won't be Mariano Rivera, there's no chance he'll be as effective as Rivera has been for so long. Still, he throws a good cutter, and gets a lot of strikeouts, making him one of the best relievers on an annual basis. Using Fangraphs pitch type value, Robertson has had the 10^th best cutter amongst all relievers in 2013 and the 8^th best since 2007. To no one's surprise, Rivera has the third most valued cutter this season, and by an incredible margin holds the top spot since 2007. In the hearts and minds of Yankees fans, no one will suitably replace Mariano Rivera, but Robertson may have the best chance of solidifying a role that most in baseball have never seen as uncertain. There's a good chance Robertson becomes the Yankees closer in 2014 and then someone else takes over the next season, but the Yankees might do themselves a favor by locking down that role now, and signing Robertson to an extension. No matter what becomes of the situation in the future, it sure seems as though the cutter won't be missed at Yankees Stadium.

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All statistics and contract details courtesy of Fangraphs Baseball Prospectus and Baseball-Reference.

Ben Horrow is a writer at Beyond The Box Score and That Ball's Outta Here. You can follow him on Twitter at @Summerpastime.

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