Scary moment at the Australian Open -- tennis star Nick Kyrgios smacked a loose ball out of frustration during a doubles match ... and it ended up nailing a young fan in the crowd.
Fortunately, the kid appeared to be OK after Kyrgios apologized with a gift racket.
The wild play all went down Monday during Kyrgios' doubles event with partner Thanasi Kokkinakis ... when Kyrgios got pissed over a missed serve.
You can see in footage from the Open, Kyrgios rifled a ball into the ground, and it ended up riccocheting straight into the stands and right into a kid's stomach.