Hitting the clock without moving In an official blitz game, what happens if a player hits a chess clock without making a move? I believe that making an illegal move in a blitz game is an automatic loss. But does this count as an illegal move because my opponent didn't really make a move?
You can only make an illegal move by making a move. Pressing the clock without moving is not making a move. So the arbiter can't use that rule to make a decision.

There is FIDE rule 6.13 (chapter 6 is about the clock): "If an irregularity occurs and/or the pieces have to be restored to a previous position, the arbiter shall use his best judgement to determine the times to be shown on the clocks. He shall also, if necessary, adjust the clock’s move counter."

So the arbiter can use his best judgement to reinstate the correct clock times. This is of course unfortunate (it's hard to stay concentrated for the players, especially the innocent player), but the arbiter can't just invent rules.

If this happens regularly (the player is doing this on purpose), there is always article 12.8: "Persistent refusal by a player to comply with the Laws of Chess shall be penalised by loss of the game. The arbiter shall decide the score of the opponent."