Light sport aircraft pilot reported a runway excursion after landing. Reportedly; as the pilot applied the brakes and then released them; the left brake remained partially engaged causing the aircraft to veer left and ended up off the runway.

Narrative

We flew from ZZZ to ZZZ1 and back to ZZZ. Takeoff from ZZZ; landing at ZZZ1 and takeoff at ZZZ1 occurred without incident. Upon our return to ZZZ; it started to lightly rain. There was about 7 miles of visibility with generally calm winds. We were instructed to enter a right downwind for Runway XX and report 3 miles out. Reported IAW direction and cleared to land. Landing was normal at approximately 58 KIAS. Attempted to allow the plane to slow the airplane without braking; but as I approached runway Delta; I applied the brakes. When I let off of the brakes; the left brake appeared to remain engaged a little (the wheel was not frozen; still rolled; but appeared to be at a lower speed than the right) causing the plane to pull left. Because of speed; I ran off the left side of the runway. When we impacted the grassy area; the left wheel started to roll again and I regained steering control. I traveled about 100 yards parallel to the edge of the runway and when clear of lights; I turned back onto the runway.I do not believe that I impacted any lights or infrastructure on the side of the runway and reported that to the tower.Exited Runway XX at Delta and was told I could taxi to hanger via Delta.Upon stopping I inspected the aircraft (no damage found on my inspection); parked it and helped my [passenger] out of the aircraft and took her home. On way home; I talked with Head of Maintenance. After I got off the phone; I texted the owner of the aircraft about the incident. Owner called me back and we discussed the incident. Owner told me he would go test fly the airplane later in the afternoon. I have heard no results from his test flight as of the time of this report.As far as I can tell; there was not damage to either the airplane or the runway infrastructure. Additionally; per NTSB Regulation 830.5 (49CFR830.5); this does not required notifying the nearest National Transportation Safety Board (NTSB) office.Personal Training Plan: Prior to flying an airplane equipped with toe brakes again; I plan to practice high speed taxi and braking and multiple full stop landings with a CFI to ensure that I have additional practice on braking.