What does "call it this time" mean? I don't understand how could this mean "choose / decide something" here.
"Call it this time" here refers to people choosing "heads" or "tails" when a coin is being tossed to make a decision. The speaker is saying that someone from each team in this scene was each supposed to shout "heads" or "tails", and then whoever correctly guesses which side the coin will land on wins. "Heads" and "tails" refers to each side of an American coin. "Heads" refers to the side of a coin with an American president's "head" on it, and "tails" refers to the other side of the coin.