It is considered a sport because you can compete in it. Canopy piloting, formations, etc.

There’s all sorts of competing that happens in skydiving. From accuracy landings to formation jumps. Here’s a video of one of the top 4-way teams competing this year. The US Nationals were just at Skydive Chicago.

Here's the United States Parachute Association page on competitions.

Here's an example of Arizona Airspeed, one of the top teams in the country, showing what relative work competition looks like.

Here's a video of highlights from this year's nationals in canopy piloting.

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