also: それゆけ
interjection
go!; go go!; get to it!; up and at 'em!
An energetic interjection used to cheer someone on or urge them to start moving, similar to 'Go!' or 'Let's go!' in English. Often used in sports, competitions, or to encourage action.
それ行け！あと少しでゴールだ！
Go! You're almost at the finish line!
試合が始まった。「それ行け！」と観客が叫んだ。
The match started. The spectators shouted, 'Go go!'
行け is the imperative form of 行く (to go), used as a direct command. それ行け adds それ for extra urging, making it more like 'Go on!' or 'Off you go!'
頑張れ is a general cheer meaning 'Do your best!' or 'Hang in there!', while それ行け is more specifically about urging someone to go or start moving.
Combination of それ (that, there) and the imperative form 行け (go) of 行く (to go). The phrase literally means 'Go there!' and has become a fixed interjection.