The ESPN commentator has been sued in Florida over an accident that occurred back in February ... and one of the alleged victims claims she was physically scarred and disfigured as a result.

But Mashburn is fighting back -- and in court docs obtained by TMZ, he denies responsibility and points the finger at his accusers ... who he says were NOT following common safety rules of the road.

In the docs, Mashburn claims both people were NOT wearing seatbelts at the time of the crash ... and alleges the driver was using a cell phone.

Mashburn also claims the alleged victims are LYING about the extent of their injuries ... insisting they were not permanently injured, scarred or disfigured.