N-COUNT
挫折；挫伤；打击
A knockback is a problem or a rejection which delays your progress or which reverses some of the progress you have made.
例句
The schedule has suffered a knockback...
该计划遭受了一个打击。
I must have made more than 100 phone calls and I didn't get a single knockback.
我一定已经打过100多个电话了，而且还没遭到过拒绝。