Champion Citabria instructor pilot reported loss of directional control after landing resulted in a runway excursion. It was later determined that the heel brake pedals had been installed incorrectly and may have contributed to the event.

Narrative

I was conducting tailwheel training in my personally owned aircraft for a private pilot. The student was flying from the front seat and I was flying from the back. We were practicing crosswind wheel landings on runway XX. Winds were reported as 190/6 but wind direction was variable. The approach to landing was normal but after touchdown during the roll out; the student's left foot became stuck between the rudder pedal and heel brake. The aircraft swerved violently to the left. I put in full right rudder and brake deflection to maintain directional control but the aircraft departed the runway to the left hand side. The aircraft entered the surrounding grass area at a relatively low speed; and I was able to regain directional control to avoid a ground loop. After the aircraft came to a stop; I assessed that neither the student nor I were injured and that the aircraft was not damaged. I made a radio call to Tower and told the Controller we were okay. The Controller said we could taxi back. I requested a takeoff from present position with 3000ft of runway remaining. We were cleared to takeoff; taxied onto the runway from the grass; and took off. We remained in the pattern for two or three more landings and then departed for ZZZ1. Tower provided me a number to call as we were departing the pattern. After landing at ZZZ1; I inspected the aircraft and found no damage. However; I did discover that the front left brake and back right brake had been swapped. The heel brake consists of a post and a tab that points either left or right; depending on whether it's for the front or back seat. Because the brake pedals were swapped; the tab on the left brake interfered with where you would place your left foot for the front rudder pedal; and caused the student's foot to become stuck between the rudder and brake. The aircraft was completely restored in 2004; and the rudder pedals were most likely unknowingly installed in the wrong spots. The front left and back right brakes will be swapped so that the brake pedals do not cause any interference.I called the number Tower gave me and provided my name; address; and certificate number as requested. I also explained what caused the aircraft to depart the prepared surface. The FAA representative I talked to said that no landing lights were damaged and that they didn't observe any damage to the aircraft.