Isaiah Rider's wife was involved in a fight with another mom at a youth basketball tournament in Arizona ... with Isaiah allegedly threatening to get his gun from his car, this according to the police report.
48-year-old Rider -- who spent 9 seasons in the NBA -- is the head coach of the SkyRiders basketball team, which was playing a tourney at the Inspire Court gym in Mesa, AZ on May 17.
Cops responded to the tournament over reports of parents fighting -- and when they got there, they spoke with Isaiah's wife, Vanessa .