Translation:When the ball hits the ground, you lose.
Looking at your tree I guess this question appeared in the Verbs: Infinitive-1 skill. I think the exercise must have been misplaced because "cair" is not the infinitive form of the verb here, it is the 3rd person singular future subjunctive form "cair" (they just happen to look identical for many verbs).
Nope .... but for most verbs, all conjugations are exactly the same.
Future subjunctives come mostly in conditionals, especially with "quando" and "se". Some typical subjunctive sentences with "que" as well. It's about possible/uncertain things.
Verbs that have different conjugations for future subjunctive and personal infinitive:
- Ir (para eu ir / quando eu for)
- Vir (para eu vir / quando eu vier)
- Ver (para eu ver / quando eu vir) - this is a killer
- Ser (para eu ser / quando eu for)
- Estar (para eu estar / quando eu estiver)
- Querer (para eu querer / quando eu quiser)
- Saber (para eu saber / quando eu souber)
- Haver (para haver / quando houver)
- Ter (para ter / quando tiver)
- Fazer (para eu fazer / quando eu fizer)