It's called "choking" or "cymbal choke". Another name for it is "muting". Unfortunately that term is overloaded since it also means putting materials on cymbals to make them sound quieter for practice or just to make them less intense.
What is it called when you grab a cymbal?
In percussion, cymbal choke is a drum stroke or push which consists of striking a cymbal with a drum stick held in one hand and then immediately grabbing the cymbal with another hand, or more rarely, with the same hand.
What is Iscymbals?
Cymbal, percussion instrument consisting of a circular flat or concave metal plate that is struck with a drumstick or is used in pairs struck glancingly together. Traditionally the best cymbals came from Turkey—their manufacture and copper-tin alloy a guarded secret. ...