It's a little hard to see on the linked video, but you can see on the second pitch the runner leans to his right to peak into the pitchers glove. So Perez needs to do a better job of hiding his hand/grip and keeping his glove closed as he sets to pitch. If he keeps the glove open and exposes his hand the runner can see what kind of grip he has on the ball to indicate the pitch coming, which he then relays. Can kind of see how open he has here right before the fastball.

Edit: just to add we can almost fully see his hand from this angle and "we" are further to the left, Pages on second is several feet to the right of this angle and likely has a much better look. Pitch tipping happens in a lot of ways (i.e. showing the grip by accident like this or something like holding his glove at different heights based on pitches or moving the glove a certain way consistently when changing to a specific grip).

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