To sit down another player means that a player has shown a piece of skill and composure to make their opponent dive in and fall to the ground. The first player then moves in a different direction to shoot or pass.

In this example, Sancho is composed (calm) and his dummy makes Milner fall down which means he can then go in the different direction to score.

https://languagecaster.com/football-language-to-sit-the-keeper-down/

Sit down the keeper is great - this shows great skill and composure from the attacker.

Sterling darted behind the City defence, then delayed, and in one movement to the right took himself away from Kompany, as well as the oncoming Hart, before turning the ball into an exposed goal.

This is from the Guardian news in 2013 when Raheem Sterling scored a goal for Liverpool against Man City - he stopped in front of the keeper and waited for the keeper (Hart) to dive (delayed) before rolling the ball into an empty (exposed) net (goal). He sat down the keeper and then scored.

To roll the ball into the net means that the player scored with a soft but accurate shot. 

In the example above the player has taken a defender and keeper out of the game so he can gently ht the ball into the net.