HANOVER, N.J. — When the M.L.S. Cup playoffs begin on Wednesday, the talent-laden Eastern Conference will claim the spotlight with its confounding, shape-shifting ways — and with several of its best coaches and players becoming something of a distraction just when the matches count most.

The changes already have altered the field, the seedings and the matchups for the playoffs. Now pending departures and expiring contracts have raised the stakes even more, especially for several of the East’s contenders who thought this might be the year they finally won their first title.

The top team in the East, the Red Bulls, arrives in the postseason with perhaps its best chance yet to end its 23-year pursuit of a championship, but also with the sobering reality that the team most likely will lose its top young player to Europe in January — after having already lost its coach midseason.

The No. 2 seed, Atlanta United, may face an even more disruptive off-season: Tata Martino, the coach who built the second-year team into an arena-filling, goal-producing juggernaut, announced last week that he would not return in 2019.