absolutely he can....the pitching position is not considered in the rule......defining a quick pitch just entails your judgment that the pitcher was trying to catch the batter off balance by throwing the pitch prior to the batter being reasonably set in the box.......
The applicable NFHS rule is 6-1-Art 1
the definitive OBR comment is below...
Rule 8.05(e) Comment: A quick pitch is an illegal pitch. Umpires will judge a quick pitch as one delivered before the batter is reasonably set in the batter’s box. With runners on base the penalty is a balk; with no runners on base, it is a ball. The quick pitch is dangerous and should not be permitted.