A sport must be a physical activity involving propelling a mass through space, it must involve competition against an opponent, it must be governed by rules that define the space, time, and purpose of the contest, and it must acknowledge that the purpose of the competition is to compare skills of the participants.
Let’s go through the standards of sports to determine if cheerleading is a sport.
Must be a physical activity involving propelling a mass through space. Stunts—lifting and throwing a flyer, a mass, through the air—is a physical activity.
It must involve competition against an opponent. In cheer, cheerleaders compete against other teams to outperform their routines and are judged on their moves, unity, stunts, and jumps.
It must be governed by rules that define the space, time, and purpose of the contest. There are score sheets, time limits, and mat size standards that define specific rules for the competition.
Finally, a sport must acknowledge that the primary purpose of the competition is a comparison of the relative skills of the participant. In cheerleading competitions, teams are judged on their skill of jumps, stunts, and ability to perform in unity. These skills are compared against other squads.
So based on the definition of sport, cheerleading is most definitely a sport.