Who is likely to fill in for Mariano Rivera next year?

I know a lot of people wish that Mariano Rivera would never retire. Joe Girardi recently expressed his wishes for a return season. I've heard many a talkinghead on sports shows echo the same sentiment, but let's get a grip here folks, this is it. He announced it at the beginning of the season. I'm sure he really wanted to end it last year if it hadn't been for that injury. He's going to be 44 years old in November! What do you want from the guy? So let's take a look at the candidates to fill in as the closer for next year.

This is something the Yankees haven't had to contemplate since spring training in 1997. I know saying ‘that's amazing' is the epitome of obviousness, but I'm still shaking my head just typing it. The Boston Red Sox have effectively had 11 different players serve in that role during that timeframe. That number would have been much higher if Jonathan Papelbon hadn't shown up. He filled the closer role for six years for Boston. Remember who the obvious replacement for him was last year? The guy who just got picked up off waivers by the Chicago Cubs: Daniel Bard. This is a very volatile position.

David Robertson is Mariano's primary set-up man, and the first choice as the heir apparent. Of course he was also supposed to fill that role last year when Mo went down for the season, but a few rough initial outings followed by an injury allowed Rafael Soriano to grab the job. The good news is Robertson has been fantastic this year. In fact, he's statistically been even better than Rivera.

The above list is sorted by WAR which I did not show as I'd rather focus on the skill sets here versus what has already been accomplished. Way back in March I wrote this article about the changing prototype of the modern closer. You can find more detail there on why I chose the above metrics. The quick review is that double digit rates in either walks, or home runs per fly ball, is problematic for the closer role. Thus, high ground ball rates are very desirable. Also, large split differentials between left-handed and right-handed batters on an OPS basis is a negative. The closer role is the one reliever that managers do not want to use match-ups against batters.

Despite Robertson's fantastic surface stats like his 1.58 ERA, his near double digit rates in walks and home runs are very close to the danger zone. He's been able to overcome those issues so far by producing a 91.3% LOB%, which is materially higher than his 81.1% career LOB%. Some would probably point to that as an unsustainable trend, but I'm going to focus on his bump up in GB%. At 48.1% it's his highest rate and well north of his career 43% rate. That's a big help in reducing the number of baseballs flying over walls, and it likely is also helping to strand more runners on base. While his walk rate still leaves a lot to be desired, it at least matches his performance from last year, and that is significantly better than the mid-teens rates he was doing in his first four years in the majors. His split differential looks a little high, but his career rate is less than half of that. So I think we can safely say for now that it's not a concern. He's not perfect, but Robertson has been getting better and deserves to be on top of the leader board.

Shawn Kelley is next in the order of set-up men to Rivera, and he has an elite strikeout rate. However, he is well into double digits on both walks and home runs. Plus he is more of an extreme fly ball pitcher. You can ask Phil Hughes how he likes pitching in Yankee Stadium if you want to consider Kelley as a dark horse. Boone Logan is clearly the lefty specialist and also has issues with walks and dingers.

So who's the dark horse out of the current bullpen? I think Preston Claiborne looks interesting. He hasn't been getting the higher leverage situations yet, and he has had trouble with left-handed batters so far this season, however, there's a lot to like here that might fit well as a closer. He nearly matches Robertson's ground ball rate and he already walks fewer and gives up significantly less home runs. His K% might look low on this list, but his rate is still higher than five other currently established closers, including Rafael Soriano. The downside is that he's been getting worse as the season has worn on. He does have a history of controlling the long ball in the minors though, which arguably might be the most important attribute for a good closer. It's one of the keys that has made Rivera so successful. I think all of that might make Claiborne an interesting dark horse for the role if Robertson should stumble next year.

Are there any players currently in the Yankee's farm system that might slide into the role next year? I don't consider Joe Girardi the kind of manager to take that kind of risk with a rookie, but the future is uncertain so let's take a look anyway.

Mark Montgomery has been considered one of the better relief prospects in the minors and has been mentioned in the past as a possible closer in the making. He has good stuff and has been putting up the numbers as he marches through the system. This year he's done ok as a 22-year-old at the highest level in the system. There's still work to be done though here, as his walk and dinger rates attest to. He is young for the level, however, and he had only given up one homer before this year in his professional career. So Montgomery shouldn't be forgotten come next year if things go wrong early.

Another interesting name in Triple-A is Sam Demel. A couple of years ago he was considered a possible closer in Arizona when he was included in a trade for Conor Jackson from Oakland. However, he had trouble keeping the ball in the park, despite his ground ball tendencies, and it still looks to be his problem this year in the minors. While, he was once considered to be a possible late inning reliever, at age 27 he's a pretty big long shot at this point.

There have already been some interesting things written here and here about Cesar Cabral and Dellin Betances. I don't have much to add about either to the discussion. In regards to Betances as a possible closer, however, the clear issue, despite his early success as a reliever, is his control.

Robertson does deserve to be considered the favorite to fill in for Rivera next year. He's made some important improvements in his game over the last two years that make him a more viable candidate than in years past. However, there are some issues in his game that could open the door for others to step in and take control of the closer job. Robertson struggled as I was writing this article on Wednesday night to the tune of one out, one walk, three hits, two runs, and allowed two inherited runners to score. His performance forced Rivera to enter the game with a one run lead in the eight. He also has more career blown saves than actual saves. I hate both stats, but you know what the focus will be on him next year.

The odds overwhelmingly favor volatility for the future closer position. That's what every other team usually deals with. Will the Yankees look to sign some veteran closer help in the off-season? It wouldn't surprise me. It also wouldn't surprise me if someone like Claiborne, Montgomery, Demel, or Betances wound up as the closer at some point next year. Enjoy the final days of getting to watch the last player to ever wear 42 play the game, but next year welcome to the reality that every other team has been dealing with since 1997.

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• Pinstripe Alley Podcast Episode 22: Come Sale away
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• How will the Yankees use Phil Hughes out of the bullpen?
• AL Wild Card race: Yankees running down the Rays