California high-schooler Manford is a genius at basketball. He’s even better at impatience. When we meet him, in director Jennifer Chang’s gripping production of Lauren Yee’s “The Great Leap” at Round House Theatre, the teenager is feverishly pressuring a university basketball coach to make a fast decision. Legs braced, as if for a heavy lift, Manford flicks through index cards jotted with talking points, his words helter-skelter, a hand gesturing frenetically when language seems too slow. The coach, Saul, who’s never seen the kid before, looks on, flummoxed: Who accosts a stranger in this way?