Spurs are beating City at halftime, for the same reason that Aston Villa lost yesterday.
There is no sane reason to play an offsides trap on a set piece. Defenders should be running away from the goal, not towards it. Offensive players always have the advantage when everyone is running in towards the goal. Manchester United gets most of their goals on crosses when defenders are facing the wrong direction, including the winner yesterday. Rooney scored an own goal a couple of weeks ago, because he was facing in.
You don’t gain anything by trying to hold the line on a set piece. Why does everyone make the same mistake? Just say no to offsides traps on set pieces.