You may be looking for Jasko.
Commander Jask was a Sontaran whom Mickey Smith and Martha Jones hunted. He was about to shoot Martha when the Tenth Doctor knocked him out by hitting his probic vent with a hammer. (DW: The End of Time)
Behind the scenes
- Jask was not named on screen or in the credits. However, his name was given in the script to The End of Time, Part 2, which is available for download on the website for The Writer's Tale.