...
During combat S and M size ships have a chance to bail leaving the ship abandoned and able to be claimed by other faction or the player. To personally claim an abandoned ship, <player> must spacewalk to it, and then locate and scan a signal leak. After the ship becomes player property, the player can dock with the ship and fly it away.
Alternatively select the neutral abandoned ship and then right click it to order a Marine working as crew onboard the player ship to go and claim the craft using a boarding pod. The used marine will then be placed as the Pilot of the new ship once ownership has been transferred. If you intend to keep the ship, finding at least a one-star pilot is recommended to replace that random marine.. or you could set them to 'explore' for several hours to level up their piloting skill..
...