expression, i-adjective
poor at preventing an underarm grip
Sumo term: describes a wrestler who is weak at defending against an opponent's underarm hold (脇).
あの力士は脇が甘いから、すぐに差されてしまう。
That sumo wrestler is weak at defending against an underarm grip, so he quickly gets his arm grabbed.
expression, i-adjective
having weak defenses; off guard; vulnerable
Idiomatic extension of the sumo term; used for people, teams, or systems that are easily exploited or caught unprepared.
彼は仕事はできるが、プライベートでは脇が甘いところがある。
He's good at his job, but in his private life he can be off his guard.
あのチームは守備の脇が甘いから、そこを狙おう。
That team has weak defense, so let's target that.
Originally a sumo term. 脇 (armpit/side) refers to the area under the arm; 甘い here means 'loose' or 'weak.' The phrase describes a wrestler who fails to keep his armpits tight, allowing an opponent to get an underarm grip. It later broadened into general use for any kind of defensive vulnerability.