RotoWorld reports today that Jack Cust will re-up with the Oakland A’s for $2.5 million, a slight paycut from his $2.8 million salary last year. Considering that he is pretty much a DH these days (-23.1 UZR/150 career in the OF), that salary seems just about right for a guy that produced 8.8 batting runs above replacement last year. The market seems to be paying under $4 million a win, and the A’s will pay about a million less than they ’should’ given those market characteristics… if Cust performs at the same level in 2010.

And there’s the rub. Fantasy owners, too, will be wondering if Cust can put up another season with a .350+ OBP and 25+ home runs – especially those owners in OBP leagues that could use a late-round value pick with some pop.

Cust has long been a “three true outcome player” in that his career walk (17.8%), strikeout (39.5%) and home run (5.8%) rates comprise the results for the bulk of his at bats. There’s been a little play in those rates as he’s aged, though. Last year, Cust put up three-year lows in walk rate (15.6%), strikeout rate (36.1%) and contact rate (69.2% last year, 66.8% career). Still, those look like enough like his career numbers to say with certainty that Big Jersey (6′1″, 240 lbs, born near Somerville, NJ) will walk, strikeout, and hit the ball hard next year.

He definitely has what most call “old-people skills.” These are skills, like walking, whiffing and swinging for the fences, that players develop more as they age. Some players begin with these skills, and most develop them, and they stand in opposition to more “young-people skills” like speed and contact that you either have or you don’t. Bill James famously found in his New Bill James Historical Abstract that players with these “old” skills peak earlier and decline faster. Here’s the money quote, taken from a passage about Tom Brunansky, courtesy Tommy Bennett and a fruitful and lively twitter conversation today:

The outfielders that had “old players skills” did in fact peak earlier and fade faster than the players who had “young players skills.” From ages 21 to 23 the two groups of players were equal in value, 614 Win Shares for the “Young” players, 615 for the “Old” players. But from ages 24-26 the players with “old” skills had 7% less value (1482-1379), and as time passed the gap widened steadily… from ages 31-33 they had 10% less value (1340-1207).

From the mouth of a legend. We can’t take that number as a lock-down predictor, but it seems safe to say that a 31-year-old Cust is at least 10% more likely to decline faster than a player with a nice batting average and tons of steals. And there are some other signs of decline there anyway: his HR/FB and line drive rates are in a three-year decline, which would be more worrisome if they weren’t still decent last year (17.7% HR/FB and 19.8% line drive rate in 2009).

So that trip down memory lane was a roundabout way to say that fantasy owners should probably not expect a “bounce-back” season from Cust, and shouldn’t draft him expecting a return to his .500 slugging percentage days. The older he gets, and the closer that home run total inches to 20, the less likely he will provide enough value elsewhere to offset his always-poor batting average. Cust is an exponentially riskier play as every year passes, thanks to starting out with “old people skills.” (In case you were wondering, Adam Dunn just turned 30.)