big leagues
An area, echelon, or sphere of great competition, success, power, achievement, etc. Refers to major (i.e., "big") leagues of sports teams. I know you're new here, but you need to perform much better than that. You're in the big leagues now. Welcome to the big leagues, senator.
big-league
Describing or indicative of the highest level of something. That's a tough injury to come back from—I wonder if he'll ever be a big-league pitcher again.