I don't think there's a way to discourage laming. Whether you're running to or from someone, you can still lame.
But you can discourage running by modifying the killstreak system into something that uses kills per minute as a metric instead of kills without deaths.
Say it rewards you based the amount of kills you got within the last 10 minutes, regardless of deaths.
You would be incentivized to rush into wherever there's a big fight and kill as many people as possible without worrying about dying.
That being said, you would still have people running because if you're trying to maximize your kills per minute, running would probably be less of a time waster than dying and running back 4 times.
I say make people spawn with full health after dying