At first glance the answer seems simple. Papelbon has 21 saves, and only 2 blown saves; he is pitching to an incredibly effective 1.70 ERA; he only has one loss. All of these stats would lead you to believe the guy is having one of the best years of his short, magnificent career. But anyone that has been watching the guy pitch all year will tell you that he is not getting batters out as easily as he has in the past. His saves seem to be taking a little extra effort. And looking at the numbers, the way he has been pitching he's lucky that his ERA is not closer to his FIP of 3.93.

Paps' control is simply not there this year. That much is obvious. Already he's matched his career high in walks for a season (17) and has walked more than twice as many guys as last year (8 BB's). His BB/9 is 4.14, more than twice is career total and 4 times the rate he was walking guys last year. 

 

So how has a guy who is putting people on base at a significantly higher rate than in the past not getting lit up? Mostly because of his entirely unsustainable Left On Base Rate of 96.9%. So of the 48 men that have rached base against Papelbon this season (probably a few more, but I'm not sure how many have reached on errors), only three of them have managed to score (and one or two of those runners must have scored once he was pulled or something because of the slightly off LOB%). A rate that high is a result of a run of good fortune and most likely will not sustain for the second half of the season.

There appears to be a few contributers to the higher walk rate. One, he is simply throwing less pitches inside the strike zone. This year only 49.5% of his pitches are inside the zone, compared to 57.1%, 55.9% and 54.5% in his three dominant seasons. Also, batters are chasing fewer pitches outside of the zone this season, swinging at only 26.6% of pitches thrown outside the K-Zone, compared to 29.5%, 31.3% and 34.3% in the previous three seasons.

These two are most likely related. Batters realize that he is hitting the strike zone less, so they swing less in general, as shown by a significantly decreased Swing%. So what has happened to Paps' control? I have no clue, but I do know that at some point it will catch up to him. A pitcher simply cannot walk as many people as Paps' this year and expect to be successful. A walk rate around 4 BB/9 is more similar to someone like Jose Mesa, a guy who regularly saved 40 games per year, but blew 7 or 8 in the process. That is simply not acceptable, and hopefully Paps figures it out before he starts actually costing the Sox games.

Obviously there is not anything the Sox should do about this. His 3.93 FIP is still very good, but it is simply a long way off from the low 2 FIP's that he has put up in the past. Basically this year he has pitched more like a Jose Mesa in his prime than a Mariano Rivera in his prime. And luckily this season the Sox have enough great pitchers in the bullpen that they have themselves covered in case he does blow a few saves.

 

Nota Bene:

Paps has only pitched 37 innings this year. That is not very many and there is a chance that all of those walks are just statistical noise. Last night's outing, where he struck out the side and did not walk anyone lowered his FIP by .3 or so. So all it takes is a few innings like that and Paps' numbers would be right back to his career norms.

Also, I was going to mention something about how he is no longer throwing his Splitter, but I'm not sure that is true. PitchFx seems to think that he has replaced the splitter with a two-seam fastball, but the Baseball Info Solutions data that FG's carries on its "Season Stats" pages is still recording 10% of pitches as splitters. What I suspect is that he is throwing that splitter differently and it is confusing the computers that keep track of these things. If that is the case, maybe his inability to locate the splitter is causing many of these walks? I am not really familiar enough with these computer systems and algorithms to draw any conclusions about any of that.