keep (someone or something) back

idiom

1

: to not allow (someone) to go near something

The police kept the spectators back.

2

US : to not allow (a student) to advance to the next grade level

—usually used as (be) kept back

Students who fail the exam may be kept back a year.

3

British : to require (a student) to stay at school after classes have ended

She was kept back for talking in class.

4

: to not allow (something) to appear or be known

He struggled to keep back his tears.

The government kept back some crucial information from the media.