A Sydney man has been charged with assaulting an officer after he allegedly blew his nose at a policeman while at a Red Hot Chili Peppers concert in the Hunter Valley.

The 25-year-old Kensington man was asked by security to leave the event, held at Hope Estate in Pokolbin on Saturday night, for being drunk.

Flea of the Red Hot Chilli Peppers performs at Hope Estate in the Hunter Valley on Saturday. Credit:Paul Dear

When the man allegedly refused to follow directions, police were asked to assist.

While officers were escorting him from the area, the man "allegedly blew snot at a male senior constable", police said in a statement.