Well...technically it is - but the ref can also "impose a penalty depending on his judgment of the conduct" on other infractions as well.
Catching the ball sort of falls under "(b) changing the position of the balls in play other than by a shot; " that might "change the game to the extent that it cannot be played fairly"
Meaning that - there is always the small chance that the cue ball might jar and stay on the table.
The "worst" penalty in 14.1 results in cue ball in hand in the house. So if the ball jars (behind the triangle lets say, with a shot in the opposite corner possible) and the shooter of the scratch catches the ball, potentially the shooter coming to the table will have a much harder shot behind the line - that corner shot might be now blocked from down table. (Because unlike other games, there is no ball in hand option)
Hard to explain, but technically it is an automatic 6.16 rule infraction under WPA
6.16 Unsportsmanlike Conduct
The normal penalty for unsportsmanlike conduct is the same as for a serious foul, but the referee may impose a penalty depending on his judgment of the conduct. Among other penalties possible are a warning; a standard-foul penalty, which will count as part of a three-foul sequence if applicable; a serious-foul penalty; loss of a rack, set or match; ejection from the competition possibly with forfeiture of all prizes, trophies and standings points.
Unsportsmanlike conduct is any intentional behavior that brings disrepute to the sport or which disrupts or changes the game to the extent that it cannot be played fairly. It includes
(a) distracting the opponent;
(b) changing the position of the balls in play other than by a shot;
(c) playing a shot by intentionally miscuing;
(d) continuing to play after a foul has been called or play has been suspended;
(e) practicing during a match;
(f) marking the table;
(g) delay of the game; and
(h) using equipment inappropriately.
Sounds like splitting hairs but this is reasoning - as far as I understand it anyways! Despite my bad explanation!
