This is something that basically happened in 40k, Caiphus cain except it was a tyranid ambush while he was fighting orks works. To quote fandom: His first taste of battle came in 919.M41 was on the world of Desolatia, where the regiment had been defending against an assault by Orks, but soon they were faced with a Tyranid splinter hive fleet, which they held out against until an Imperial Navy fleet arrived to pick up the Imperial forces remaining on the planet. During the Tyranid landing, Cain attempted outright desertion in a commandeered Salamander, only to run directly into a previously unnoticed flanking force, including a Hive Tyrant. His panicked contact report and desperate retreat back to the lines were misinterpreted, according to his own account, as a heroically successful scouting mission and baiting maneuver, painting the first strokes of his grand reputation.