According to the flight instructor, the flight departed for a night cross-country to the destination airport with a student pilot in the left seat and a student pilot in the rear seat. After completing a full stop landing at the destination airport, they taxied back to the runway to complete additional pattern work. As the student pilot began to rotate the airplane during takeoff roll, the flight instructor "saw an animal directly in front of the airplane on the centerline" and grabbed the flight controls in an effort to "miss the animal." He heard a "bang" as the airplane passed over what was later identified as a deer. The flight instructor stated that he then noticed the left rudder pedal was "looser" than normal and no brake pressure was observed in the left toe brake. After a few low passes and confirmation from the control tower that the left landing gear was not in the "normal position," the flight instructor decided to land the airplane. During landing rollout, the left wing struck the ground and the airplane came to rest on the runway. The postaccident examination by a Federal Aviation Administration inspector revealed that the left landing gear had separated, resulting in substantial damage to the left wing spar. According to the flight instructor, no mechanical anomalies were present prior to hitting the deer.