A321
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Critical
Flight Crew Returned To Gate; General Maintenance Action
Aircraft
After taxiing into position on Runway 18L; I set the parking brake and transferred control to the First Officer who was going to be the Pilot Flying. When cleared for takeoff; the First Officer released the parking brake and spooled the engines to 50% and rolled forward to the takeoff power point. The First Officer then verbally turned control back to me and said there is a problem with the rudder pedals. I continued at 50% long enough to understand what was the problem; then went to idle and advised the Tower we were discontinuing the takeoff and our intention was to taxi clear [of the runway] and evaluate. After evaluation we requested a gate and advised Maintenance and Dispatch.When the First Officer began to make minor steering inputs at the beginning of the takeoff roll; his rudder pedals were locked together (not able to move interdependently left and right) and; instead; they moved freely forward and aft instead of staying fixed at the selected position. A First Officer never utilizes his rudder pedals until actually using them during the takeoff roll. Today; a less experienced First Officer may have continued the takeoff rather than verbalizing a problem. I suggest we include a check of the rudders by the First Officer to the flight control check.
After taxiing the A321 into position and setting the brakes the Captain transferred Pilot Flying duties to the First Officer.  Upon brake release and power up for takeoff the First Officer discovered he was unable to apply independent left or right rudder inputs.  They rejected the takeoff at low airspeed and returned for maintenance.