After school, we play baseball with our classmates.
Literal
After-school we-[達] [topic-は] classmates [with-と] baseball [object-を] play
放課後 = 'after school' (放課 = the end of class + 後 = after). 級友 (きゅうゆう) = classmate (級 class + 友 friend), a slightly formal-sounding term; 同級生 is more common in spoken Japanese. と marks the companions, not the grammatical subject.