The phrase "biggest roster" refers to having the largest or most extensive group or list of individuals, particularly in the context of sports teams or events. Full definition
We have a pretty big roster of exercises, so it's a little hard to be too specific here. (wellroundedny.com)
SENRAN KAGURA Hits PlayStation 4 and «PSVita» with a New, Parallel Dimension Paradise Adventure Featuring Biggest Roster and Most Content in Series History; Limited «Endless Summer» Edition Includes Two Soundtrack CDs withRead More... (xseedgames.com)
Maybe NH wants bullpen to feel a little more urgency about who gets to stay on bigs roster. (sbnation.com)