Quick answer: there's no single date cheer "became a sport" - it shifted gradually from the mid-20th century onward as judged competitions developed, and this shift is still ongoing today through official sport recognition processes with bodies like the International Olympic Committee.
A Gradual Shift, Not a Single Moment
Unlike sports with a clear founding date, cheerleading's transition from sideline crowd support into a competitive sport happened gradually, as more skill-based elements (jumps, tumbling, stunts) were added and organisations began running events that judged squads directly against each other. See How Did Competitive Cheer Develop? for that fuller story.
Televised Competition Raised the Profile
From the 1980s onward, televised competitions significantly raised competitive cheer's public profile in the United States, presenting it clearly as a skill-judged activity in its own right rather than an accompaniment to another sport.
Formal Sport Recognition Is a Separate, Ongoing Process
Being widely understood as a competitive sport is different from formal recognition by major sporting institutions. Competitive cheer's governing bodies have pursued official recognition - including from the International Olympic Committee - as a distinct, later process from the sport's grassroots growth. See Cheerleading and Olympic Recognition for where that stands.
Where Things Stand Today
Competitive cheer is widely treated as a sport by governing bodies, competition providers, schools and increasingly by wider sporting institutions, even as some formal recognition processes continue to develop.
A Note on Dates and Sources
Recognition milestones and dates can change and are actively evolving. Where current, precise status matters to you, we recommend checking directly with the relevant governing body - see our sources page.