This might be hard to believe, but Sean Marshall has probably been better than most Chicago Cubs fans think this season.

Marshall, who turned 28 last month, has had a marvelous season in the Cubs’ bullpen in 2010.

His 6-5 record reflects the confidence both Lou Piniella and Mike Quade have shown in Marshall, using him in tie games 21 times and on back-to-back days 25 times.

Yet there are numbers in Marshall’s stat line this season that leap off the page unexpectedly.

He has nearly 11 strikeouts per nine innings, good for 13th in baseball. Largely because of that newfound whiff ability, Marshall also boasts a 2.37 FIP—tied for ninth in the league. 

The strikeouts are well documented: a career-high 85 of them, despite having thrown fewer than 70 frames so far this year. Many fans, however, have not yet taken note of Marshall’s much-improved ground-ball rate.

Until 2010, Marshall had been susceptible to the long ball, allowing 1.2 of them per nine innings in his first four big-league seasons.

This season, that number is 0.39 per nine frames, mostly because Marshall has induced ground balls on over 50 percent of his batted balls. It is the first time in his career that has been true.

Part of the reason is that Marshall’s curveball use is at an all-time high; Marshall gets tremendous tilt and keeps his curve down well, forcing ground balls.

Marshall’s slider had long been a problem, often flattening out and staying up in the zone to left-handed hitters. He has used the slider much less this season, with great results.

To make up the difference, Marshall has ratcheted up his fastball use and has found some velocity on that heat for the first time in his major league career. He now averages over 90 miles per hour on the fastball this year, after averaging scarcely 87 the season before.

That has helped him become such a strikeout force, and he has gotten misses on 10.3 percent of opponents’ swings this year after averaging narrowly more than eight percent whiffs in his career before this season.

If we accept—and it seems fair to do so—that Marshall will be the kind of pitcher he has been this season for the foreseeable future (meaning not that his numbers will always be this pretty, but that he now seems to have two plus pitches and enough command to use them to their full effect), it is time to ask an urgent question: Should the Cubs lock him up now?

In a word, yes.

Marshall will be eligible for arbitration in both 2011 and 2012, and if Chicago is unable to tie him up for the next two years this Winter, he could cost them serious money next year.

Right now, Marshall is not a closer, which immediately mitigates his arbitration value. To illustrate the point, compare Marshall to Dodgers southpaw hurler George Sherrill.

Like Marshall, Sherrill got less than $1 million in his first arbitration-eligible season.

After one year of full-time closing duty, however, Sherrill received $2.75 million, and that number shot up to $4.5 million the next year with Los Angeles.

If the Cubs can lock up Marshall for the next three seasons at $2.5 million per year, they will have successfully avoided the Sherrill pitfall.

Marshall still has good years ahead of him, especially as a left-handed pitcher. In a tandem with Carlos Marmol at the back of Chicago’s bullpen, Marshall could be a strong contributor for the long-term at Wrigley Field.

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