The coach of the Atlanta Braves, Roger McDowell, has been accused of shouting homophobic slurs at fans during a match last Saturday.
During the game at the AT&T Park in San Francisco, he allegedly asked three Giants fans: “Are you a homo couple or a threesome?”
He reportedly made lewd gestures at them and threatened another fan with a baseball bat.
American lawyer Gloria Allred was in the stands with Giants fan Justin Quinn and his family.
She said Mr Quinn asked Mr McDowell to mind his language in front of children. Mr McDowell allegedly responded: “Kids don’t [expletive] belong at the baseball park.”
Ms Allred claimed that the coach then walked towards Mr Quinn with a baseball bat, asking: “How much are your teeth worth?”
In a statement, Mr McDowell said: “I am deeply sorry that I responded to the heckling fans in San Francisco on Saturday. I apologise to everyone for my actions.”
Mr Quinn has demanded an apology, a fine for Mr McDowell and an order for him to attend sensitivity training.
The Atlanta Braves said: “This in no way represents the Braves organisation and the conduct we expect of our employees.
“We will withhold further comments until we finish gathering information.”
The Gay and Lesbian Alliance Against Defamation said “real disciplinary action” must be taken.
President Jarrett Barrios said: “McDowell’s apology is a start, but the Atlanta Braves and Major League Baseball must take real disciplinary action and send the message that anti-gay slurs have no place in sports.
“Professional sporting events should be an environment that all fans and families can enjoy, not a place where children are exposed to violent threats and discriminatory language.”