1.lag behind是可以的
例“：Several players began to lag behind even at the beginning of
the race.
比赛刚进行就有几名选手落在了后面.
2.leave behind 确实是遗留的意思,be left behind 可以解释为落后,但leave behind不可以
3.fall behind可以
例：
Boris is falling behind all the top players.
鲍里斯正落后于所有的顶尖选手.