подтягиваться

Hi :)

I was playing a video game on my mobile when I noticed a leader of a Russian alliance wrote this message on their banner -> Отстающие подтягивайтесь!!!

There is a lot of alliances in the game. The maximum number of people is 30 for each alliance.

Does the leader tell the weaker players to improve themselves or does he simply encourage them? I'm not sure if the message is positive or negative :)

Подтягивайтесь could be an invitation to the game for hesitating potential players.
Otherwise if the game is in the progress, then it is a call to pull together.