Its NOT an illegal kick. There are only a few of those: scrimmage kick beyond the NZ, return kick, kicking a ball that isn't teed properly, etc. Everything else illegal would be illegally kicking the ball, and its not that, either.
Don't mean to hijack this, but its way past time to put an end to the distinction between illegal kicks and illegally kicking the ball. Drop the former and put everything in the latter.