What Bill McCurdy said above - Some gun clubs hold action pistol matches which are USPSA 'like'. They have a course of fire that you shoot on the move but, the club may have it's own rules on how you can shoot and engage the targets. And, there are usually not the same rules on guns, mag capacity, equipment, etc. as with USPSA. Boston Gun and Rifle held action pistol matches for years until a couple of us formed Boston Urban Action Shooters, affiliated with USPSA and started holding USPSA sanctioned matches. For USPSA matches, the club has to allow you to follow USPSA rules. Scores are uploaded to USPSA and you earn a USPSA classification. Mystic Valley has also held 'action' pistol shooting matches for years which are not USPSA affiliated. Several years ago Boston Urban Action Shooters moved their USPSA matches from Boston to Mystic Valley so now, in addition to the Friday night 'action' pistol match, there is also a sanctioned USPSA match on the 2nd Sunday of the month November thru April.
As for the holster question -
5.2.7 Competitors must not be permitted to commence a course of fire wearing: 5.2.7.1 A shoulder holster or “tie-down” rig (visible or otherwise), except as specified in Rule 5.2.8. 5.2.7.2 A holster with the heel of the butt of the handgun below the top of the belt, except as specified in Appendix D, or otherwise indicated in Rule 5.2.8. 5.2.7.3 A holster with the muzzle of the handgun pointing further than 3 feet from the competitor’s feet while standing relaxed, 5.2.7.4 A holster which does not completely prevent access to, or activation of, the trigger while holstered.
* if it doesn't say you can't in the rules, then you can......