drop back, drop behindvi phrasalphrasal verb, intransitive: Verb with adverb(s) or preposition(s), having special meaning and not taking direct object--for example, "make up" [=reconcile]: "After they fought, they made up."
(fall behind)
落后 luò hòu
Towards the end of the race, Stacey was becoming tired and started dropping back.