What caused the unprecedented five-game winning streak?

Richmond enjoys an unprecedented five-game winning streak with Zava on the team, culminating in a win away at Old Trafford against Manchester United. Sam takes the team to celebrate at his yet-to-open Nigerian restaurant, Ola's. Ted is disturbed to learn that his ex-wife Michelle is dating their former couple's therapist, Dr. Jacob; both Sharon and Sassy validate his concern that it is an ethical violation. Jamie feels overshadowed by Zava's stardom; Roy offers to train him. Rebecca visits her mother's psychic Tish, who tells her she will one day be a mother; Rebecca angrily rebuffs Tish as a fraud, but is later stunned when Sam hands her one of the green matchbooks he is giving out to the team, in line with one of Tish's premonitions. Colin introduces his boyfriend Michael to the team as just a friend, but Trent spots them kissing in private while leaving the restaurant.

While we don't know exactly what caused the winning streak, it seems clear that a key part of the winning streak was related to Zava being on the team. We know that Jamie is overshadowed by Zava's stardom which tells us that Zava is a star, and we see that Zava was mentioned in relation to the winning streak. Therefore, we can guess that Zava joining the team helped the team to go on a five-game winning streak.