Here you can find a detailed list of game mechanics.
"Lockdown" mechanic[]
Lockdown
The Lockdown mechanic is timer based counter which starts from 3 minutes and counts downwards towards 0.
A lockdown occurs when one side has failed to capture an objective for an extended period of time.(Usually around 10 minutes) When a lockdown reaches 0, the attacking side will lose regardless of their tickets and match time limit.
Overtime
The purpose of this mechanic is to try and avoid a draw-out stalemate and also an attempt to force the attackers into pushing to break said stalemate.
If a lockdown reaches 0 but members of the attacking team remain in an objective and are contesting it, the timer well go into "Overtime" which means the defenders must clear the objective before the timer will end the round and allow the defenders to win.
If an objective is captured in Lockdown or Overtime, the timer will be stopped and the round will play on using tickets and the match timer.