Oh well... BCAPL rules conflict with WPA rules
Aside from the BCAPL rules below... I have always played that any ball in the kitchen is unplayable unless you hit a rail first.
WPA world rules say otherwise and conflict with BCAPL rules.
http://www.playbca.com/Downloads/Rulebook/CompleteRulebook.aspx
OFFICIAL RULES OF THE BCA POOL LEAGUE
1-36 Shooting with Ball in Hand Behind the Head String
5. Situation: Player A calls the 1-ball in Pocket A, and then shoots from position C3, cutting the 1-ball into Pocket A. The cue ball is past the head string when it contacts the 1-ball.
Ruling: Foul. The 1-ball was behind the head string and was the first ball
contacted by the cue ball. The cue ball did not contact a cushion at a point
below the head string before contacting the 1-ball, nor was the cue ball's first
contact with a ball below the head string.
The fact that the cue ball crossed the head string before contacting the 1-ball is irrelevant.
See Figure 10-13. It has the exact set up as the OP.