to seem bitter (over); to appear vexed; to be resentful; to appear to regret
試合に負けた選手は、悔しがった。
The player who lost the match showed her frustration.
彼はミスを悔しがっていた。
He was visibly upset about his mistake.
負けても悔しがらないコーチは、選手を育てられない。
A coach who doesn't show vexation over losses cannot develop players.