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Looking at B-Ref's Similar Players for Bourn and Pence

The off-season has brought occasional discussion around here about the future of Michael Bourn and Hunter Pence.  No one has a crystal ball, so no matter what kinds of opinions are thrown out there, nobody can be proven wrong.

One interesting way of thinking about player's future career path is to examine the path of players with a similar comparability score.  The similarity scores at are derived from the original concept devised by Bill James many years ago.  The concept, itself, has led to various offshoots used by projection systems to identify comparable players. Some would argue (perhaps correctly) that B-Ref's similarity scores are less sophisticated than those used by PECOTA or ZIPS.  But that's besides the point, since the exercise in this article is more for "fun," than prediction.  That's not to say we can't glean some kernels of information relevant to Bourn and Pence.

Two players are tied for "most similar" to Bourn: Bill North and Brett Butler.  The similarity score (971) through age 27 are fairly high.  North, who was very fast, has the distinction of being the starting CFer on the first A's world championship team of the 70's.  (He also gained fame for getting in a clubhouse fight with Reggie Jackson.)  North had a 10 year career, playing his last year at the age of 33 in 1981.  North had a career OPS+ of 99, and peak WAR of 6.4 and 5.3 in 1973 and 1975.  Brett Butler was one of the best CFers of the 1990s, and has one of the longest careers you will find for a slap hitting style speedster.  He had a 16 year career as a CFer with peak WAR of 6.0 in 1988 and 5.0 at age 35 in 1992.  Butler's final season was at the age 40, retiring with a career OPS+ of 110.  Brett Butler's performance was remarkably consistent over a long career.  I recall baseball broadcasters of the late 80's and early 90's marveling over his ability to disrupt the other team's defense with his speed.  I don't trust the defensive metrics applied to 30 year old box scores.  However, the fact that both players continued to play CF over their careers indicates to me that their defense aged well.  Both North and Butler showed the ability to be productive base stealers throughout their careers, including the final years.

Both North and Butler had good careers.  But, given a choice, Butler's career path is superior to North's.  While Butler isn't a Hall of Fame player, he would get a spot in most people's Hall of Very Good, mostly due to his longevity in consistent production as a lead off hitter.  It's unclear why Butler extended his career so much longer than North.  Both players have very good career walk rates (11.8% for Butler and 13.6% for North) and virtually no power (career ISO well below .100 for both players).  The walk rates point out the fallacy that slap hitters cannot sustain high walk rates (how many times do you hear fans say that pitchers have no reason to throw anything but strikes to players without power?).  Bourn's career walk rate is decent but falls below the level set by Butler and North.  Bourn was able to sustain walk rates similar to Butler and North in the minors; so maybe he can improve his ability to draw free passes. 

I'm not aware of any factors, like injury, which caused North to have a shorter career than Butler.  However, perhaps one statistical difference between the two players tells us something.  Butler has a career BB/K rate above 1.  Despite drawing walks at a higher rate, North has a career BB/K rate below 1.  North and Bourn share the propensity for high strike out rates.  Undoubtedly this hurts a player's ability to maintain a consistent batting average.  North has a significantly lower career BABIP than Butler.  And I suspect that North's declining batting average in the last three years of his career (.259, .251, .221) led to the end of his career.  In his final year, North's BABIP dropped to .271 and his K rate spiked to 22%.  Given that he was not at a prime age, some bad luck on his BABIP could have ended his career.

Although data on bunt singles doesn't go back to that era, I suspect that Brett Butler's bunting ability helped him maintain a consistent BABIP and reduced K rates.  Butler had the reputation as a hitter who could get a bunt single at will.  Bill James called him the best bunter of the 90's.    Bourn indicated before spring training that he needs to improve his bunting skills.  If the Butler comparison means anything, that's probably a good idea.

The two most similar players through age 27 for Hunter Pence are Bobby Higginson and Aubrey Huff, with similarity scores of 968 and 965.   (For players of the same generation as Pence, Matt Kemp and Corey Hart are the most similar players.)  Higginson had a shorter career than Huff; Higginson's OPS+ fell off a cliff at age 32 and he was out of baseball two years later.  Apparently, Higginson suffered an elbow injury late in his career, and that probably contributed to his decline.  Huff is still going at age 34, re-signing with the Giants after posting one of his best OPS+ seasons (138) for the World Champions last season.  Two years ago Huff posted a career worst OPS+ of 89 and one might have thought his career was about to tumble precipitously, but it didn't.  Huff has never been considered an above average defender, but he was versatile with the ability to play both corner OF positions, 3d base, and 1st base.  (You may remember that Huff split time between 3d base and RF for the 2006 Astros.)  Despite his reputation as a weak fielder, Huff's versatility probably helped extend his career.  Higginson at his peak was considered a very good defender in the outfield.  However, his arm injury probably hurt his defensive ability late in his career, and he apparently did not have the ability to move to the infield.

Huff's walk rate is more similar to Pence, which is to say, that it is average to below average.  Higginson's walk rate was above average, which made him an elite .392 wOBA hitter in his best year.  Huff and Higginson both have similar strike out rates to Pence, i.e., about average for power hitters.  Higginson had a better peak than Huff, but he has the classic high peak followed by rapid decline career pattern.  Higginson's best OPS was at age 25 (145) and age 29 (134), with good seasons bunched between those ages, but his OPS+ declined rapidly in the four years after age 29.  Huff's OPS has bounced around over his career, with both early career (age 25/26) and late career (age 33) peaks.  Huff also has below average seasons which created a sense of inconsistency.

Another factor which may have extended Huff's career longer than Higginson is his higher career power.  Huff has a career ISO of .199 and Higginson, .183.  Higginson's ISO went into a precipitous decline after age 30.  Power is an "old player skill" which can make a player more valuable in the late stages of his career.

I'm not sure that tells us much about Pence.  But it would be helpful if Pence could improve his power.  Although Pence has extreme consistency in HR power (25 for three consecutive years), his doubles have shown some year to year decline.  I think Pence could become a 30 HR hitter, but his other extra bases without depend on some degree of luck, plus perhaps an improved LD rate.