crash the gate

To attend an event, such as a concert, sports match, or party, without being invited or paying to get in. That's way too much money to see them in concert, let's just crash the gate and see them on the sly! There's always a few who crash the gate at my party and end up causing trouble.

Gain admittance, as to a party or concert, without being invited or without paying. For example, The concert was outdoors, but heavy security prevented anyone from crashing the gate. This term originally applied to persons getting through the gate at sports events without buying tickets. By the 1920s it was extended to being an uninvited guest at other gatherings and had given rise to the noun gatecrasher for one who did so. [Early 1900s]