I was having a quick look at Greene's FanGraphs page the other day, and it struck me (as it has done every time I've looked at his stats in the last couple of years) what a truly exceptional base-stealer he is, potentially even verging on the "great" in this regard. The unfortunate thing about Greene is that he's a real bit of a mishmash of uncomplimentary talents - plenty of power for a shortstop, but serious contact problems, and exceptional speed and instincts on the basepaths, coupled with an unfortunate propensity for making outs before he reaches first base (career MLB OBP of only .307 in 359 PAs), but this doesn't necessarily detract from the fact that, in isolation, his stealing stats are genuinely exceptional.
It's been pretty well-documented in recent years that stealing bases is only actually valuable if you can do it without giving away too many outs doing so - taking, for example, Vince Coleman's 1988 season - 81 SB is a hugely impressive number, but when you also take into account the fact he was thrown out 27 times attempting to swipe a bag (which means that 15% of the time he got onto first base, he actually made an out on the basepaths), the final analysis is that his basestealing wasn't that productive in that particular season.
It's been pretty well-documented that the "break even" percentage, at which the benefit of advancing a base starts to outweigh the cost of giving up an occasional out, is a success rate of about two-in-three stolen base attempts. So, a guy who swipes 20 bags per season but gets thrown out 10 times on the basepaths isn't really adding anything more to the team (ignoring the small benefits of creating possible throwing errors and being able to steal a base in a close game) with his running game than a guy like Jim Thome, who averages less than 2 stolen base attempts per year for his career. Indeed, unless you're stealing a LOT of bases, there's really only pretty marginal value to guys who have lower than an 75% success rate. To put that into context, in the history of baseball (at least since SB and CS started to be counted) there are only 16 players with more than 300 SB and a success rate of 80%+.
So the guys who can steal a LOT of bases, with a HIGH success rate, are the ones who really benefit a team - take Ichiro and his remarkable 2006 season. 45 SB from 47 attempts, or a 96% success rate. You can basically turn those 186 singles he hit that year into 141 singles and 45 doubles.
Greene has, by any standards, a fine record of base-stealing success rate. He's quick, but has great instincts as well, hardly ever getting thrown out (which, at the major league level, is even more impressive, given that many of his appearances this year have come as a pinch runner). Take a look at his numbers from his short MLB stint, and his longer career in AAA:
SB%: Infinity (Greene has never been caught stealing in the major leagues).
Greene combined totals:
89% SB success rate.
He steals a base every 18.6 PAs.
A quick comparison of these rates to some of the best base-stealers, statistically, of the modern game shows that Greene is right up there with them. In fact, his only problem (as I touched on at the beginning) is his inability to get on base. Compared to the Ichiros and Beltrans of the game, Greene's OBP is always going to be poor, and it's that which will presumably prevent him stealing a lot of bases (say, having a 40+ season) or being considered in the same breath as some of these guys.
Carlos Beltran career:
88% SB success rate
SB every 26.3 PAs
81% SB success rate
SB every 19.1 PAs
Carl Crawford career:
82% SB success rate
SB every 13.8 PAs
Jimmy Rollins career:
83% SB success rate
SB every 20.3 PAs
Jose Reyes career:
80% SB success rate
SB every 13.1 PAs
When you focus purely on base-stealing capability, Tyler Greene is right up there with the best in baseball. If his slightly mismatched hitting and fielding skills can coalesce into something that makes sense as a major league ballplayer (and despite being a fan of his, I'm by no means certain that this can happen), his ability on the basepaths will be his one truly elite skill.