Answer:
lastimé
Step-by-step explanation:
Ayer, mientras jugaba béisbol, yo me caí y me lastimé
Translation:
Yesterday, while playing baseball, I fell and got hurt
The verb "lastimar" (infinitive) conjugated in the simple past perfect indicative is used, because it refers to an activity in the past. In addition, the conjugation person is the first person of the singular ("I")