in the bullpen
1. In the area where relief pitchers warm up before entering a baseball game. Elliot is warming up in the bullpen right now, so he'll come in and try to hold this lead.
2. By extension, a team's relief pitchers taken collectively. OK, who do we have in the bullpen this season?
3. Ready and available to do something. Don't worry, I've got a few interns in the bullpen to help me with this.
be in the bullpen
To be in the area where relief pitchers warm-up before entering a baseball game. Elliot's in the bullpen right now—he'll come in and try to hold this lead.