With shortstops, a low batting average typically means a bad season, at least the plate. Shortstops tend to not have much power, and therefore also tend not to walk very much.
Rollins is an exception this year, with a roughly average wRC+ and OPS, despite a batting average that has been low for most of the year, and recently has hovered just below .240.
But his power has rebounded from a down year last year, he's walking more than ever, and he is still a very effective baserunner. So his hitting overall is still ahead of batting title contender Revere (98 wRC+ vs. Revere's 94), although Revere's baserunning allows him to surpass Rollins in total offensive contributions. Rollins has 2.7 fWAR so far (on pace for 3.4 for the year), making him the 3rd best shortstop in the NL this season.
All of which makes one wonder, what are the best seasons shortstops have had despite a batting average that low?
We are going to limit this since 1920, and in those 95 years, there have been 232 qualifying seasons by shortstops with a batting average under .240. Only seven of those seasons finished with a higher OPS than Rollins' .699.
Coincidentally, the shortstop with the two highest-OPS seasons since 1920 with an average under .240 is Jose Valentin, father of Jesmuel Valentin, whom the Phillies recently acquired in the Roberto Hernandez deal.
Using wRC+, which adjusts for a player's home park and his league's offensive environment, makes Rollins' 2014 rank even higher. No shortstop since 1920 has had a higher wRC+ than Rollins' 98 when batting below .240:
Adding in a player's other contributions in the field and on the bases gives us WAR, and Rollins' projected 3.4 fWAR for the year would be the 6th best season overall since 1920 by any shortstop hitting below .240:
Borrowing from the baseball-reference version of Wins Above Replacement, another way to look it is by offensive WAR, and Rollins is projected to finish the season with 3.6 oWAR.
That would tie Bert Campaneris' 1972 as the best offensive season since 1920 by any shortstop with a sub-.240 average.
3.6 - Jimmy Rollins 2014 (projected)
3.6 - Bert Campaneris 1972
3.0 - Jose Valentin 2003
2.8 - Dick Schofield 1988
2.6 - Bobby Crosby 2004
2.6 - Ozzie Smith 1980
(One more Phillies connection in that list of course is Dick Schofield, uncle of Jayson Werth.)
Rollins has slowed somewhat in recent weeks, but he is still having a good season, and historically so for a shortstop with such a low batting average.