In this mode, one player must hold on to a flag for as long as possible, while his teammates defend him and the flag. Teams are awarded points for killing the enemy. However, the team holding the flag receives double points towards the match score.
In order to hold the flag, the player must kill the enemy player currently holding the flag, then take the flag off their body. The player that is holding the flag will get assist points. The team to reach the score limit, or have the highest score when time runs out wins.
It's a lot like Team Defender from Modern Warfare 3.
As for the other leaked game mode "Frenzy" I haven't the slightest clue. But if I had to guess, I would say it's like a gun game, or a cycling gun game.