miser; penny-pincher
Refers to a stingy person who is reluctant to spend money. Somewhat colloquial and may carry a negative connotation.
彼は握り手だから、食事代を払いたがらない。
He's a miser, so he doesn't want to pay for meals.
sushi chef who makes nigirizushi
Specifically refers to a person who shapes nigirizushi by hand. This usage is less common than the miser sense.
あの店の握り手は、長年の経験がある職人だ。
The sushi chef at that restaurant is a craftsman with many years of experience.
握り手 is sometimes used as an old-fashioned term for the handle of a tool.
Compound of 握り (にぎり, 'gripping') + 手 (て, 'hand' or 'person'). The miser sense likely derives from the image of tightly holding onto money. The sushi chef sense comes from the action of hand-forming sushi. The handle sense is an abbreviation of 握り.