How To Handle Opponents With Excessive Swings?

The short answer is: Warning, followed by a Stroke next time.

The longer answer is:

12.10 The Referee shall not award a stroke to a player who causes interference with an excessive swing.

(G15) 17.2 Offences with which the Referee shall deal under this rule include audible and visible obscenities, verbal and physical abuse, dissent to Marker or Referee, abuse of racket, ball or court and coaching, other than during the interval between games. Other offences include significant or deliberate physical contact (Rule 12.12.1), excessive racket swing (Rule 12.4), unfair warm-up (Rule 3.2), late back on court (Rule 7.4), dangerous play or action (Rule 16.3.1.3) and time-wasting (Rule 7.6).

(G16) 17.3 The Referee shall apply one of the following penalties for these and any other offences.

Warning (called a Conduct Warning).

Stroke awarded to opponent (called a Conduct Stroke).

Game awarded to opponent (called a Conduct Game).

Match awarded to opponent (called a Conduct Match).