Specialization rules in modern bullpens.

The most prominent role belongs to the closer, the pitcher designated to retire the game's final three batters. Some left-handers serve as matchup guys, entering the game to deal with an opposing left-handed batter. Then there is the setup man, a closer before the closer, used to work through the eighth inning.

The Pirates had one of the best setup men in baseball last season in Jason Grilli, but he has graduated to the closer's role, leaving an opening multiple relievers could fill. Mark Melancon, Tony Watson and Jared Hughes lead the pack of late-inning options that manager Clint Hurdle could use to bridge the gap to Grilli.

"There's experience there with Melancon," Hurdle said. "We love the development of Hughes, we love the development of Watson."

Roles change frequently in bullpens, often with good results.

The Detroit Tigers' Phil Coke replaced Jose Valverde without missing a beat in the playoffs last year, saving two games in four American League Championship Series appearances.

Jonathan Broxton, a former closer with the Los Angeles Dodgers, twice returned to that role last season after being a setup man. He replaced Joakim Soria with the Kansas City Royals, and temporarily took over for Aroldis Chapman after being traded to the Cincinnati Reds.