THE RPTR'S HEEL CAUGHT ON A HEEL PLATE CAUSING THE ACFT TO LEAVE THE RWY.

Narrative

DURING PREFLT OF THE C172; I NOTICED THAT THE METAL HEEL PLATE (ABOUT 8 INCHES BY 9 INCHES) WAS BENT UP AND PREVENTED ME FROM OPERATING THE RUDDER/NOSEWHEEL PEDALS PROPERLY. I BENT THE PLATE BACK DOWN AND DEPARTED TO THE PRACTICE AREA. BEFORE RETURNING I DECIDED TO DO 1 TOUCH- AND-GO AT TTN. I RECEIVED CLRNC AND MADE A NORMAL APCH. AS I TOUCHED DOWN; THE HEEL PLATE APPARENTLY CAUGHT MY R SHOE OR TROUSER LEG; WHICH PREVENTED ME FROM OPERATING THE R PEDAL FULLY. I PUSHED FORWARD WITH BOTH FEET TO TRY AND RELEASE MY FOOT; BUT I MANAGED TO DEPRESS MORE L PEDAL THAN R PEDAL. AS A RESULT; THE AIRPLANE GNDLOOPED TO THE L SHARPLY AND EXITED THE RWY ONTO THE GRASS. I THEN STEERED STRAIGHT AS BEST I COULD AND ALLOWED THE GRASS TO SLOW AND STOP THE AIRPLANE. I WAS NOT INJURED; AND THERE WAS NO DAMAGE TO THE ACFT OR TO SURROUNDING PROPERTY. I REMOVED THE HEEL PLATE; THEN DEPARTED TO 39N. I SHOULD HAVE REMOVED THE HEEL PLATE DURING PREFLT OR HAVE INSISTED ON RENTING ANOTHER ACFT. I AM NOT ABLE TO DISCOUNT THE POSSIBILITY THAT I MAY HAVE DEPRESSED THE L BRAKE PEDAL INSTEAD OF ONLY THE RUDDER PEDAL; WHICH WOULD CAUSE A GNDLOOP AS WELL. THERE IS NO DOUBT IN MY MIND THAT I COULD HAVE PREVENTED THIS INCIDENT WITH A BETTER PREFLT OR PERHAPS MORE FOCUS ON OP OF THE PEDALS. ONE THING I DID DO CORRECTLY WAS TO COMPLETE A PRELNDG CHKLIST; WHICH REMINDED ME TO SECURE MY SHOULDER HARNESS. THIS PARTICULAR C172 HAS A 'SNAP-ON' SHOULDER HARNESS; WHICH CONNECTS TO THE LAP BELT BUCKLE. THESE SHOULDER HARNESSES OFTEN COME LOOSE DURING FLT. AS I BOUNCED ACROSS THE ROUGH GRASS SURFACE; MY CHEST STRAINED HARD CONTINUALLY AGAINST THE SHOULDER HARNESS. THE HARNESS PREVENTED MY HEAD FROM STRIKING THE DASHBOARD.