。
The stadium was packed with excited spectators.
Literal
Baseball-field [topic-は] excited-[past-modifier-た] spectator [with-で] full was.
興奮した is the past form of 興奮する ('get excited') acting as a prenominal modifier — 'excited (by now) spectators.' This is the stative past use of ~た, describing a resulting state rather than a past event. いっぱい ('full, packed') takes で for the filling material.