Allred tells TMZ ... the coach used "homophobic words and sexually suggestive vulgar behavior," simulating sex between gay men.
Allred says the comments and gestures were directed at 3 men whom the coach apparently thought were gay.
One of the fans, who brought his 9-year-old twin girls to the game, protested to the coach ... and according to Allred, the coach responded by saying, "Kids don't f**king belong at the baseball park." She also claims the coach then approached the father "with threatening words and a baseball bat."
Allred will hold a news conference with the father and his twins at her L.A. office on Wednesday at 1 PM PDT.
We'll be live streaming.