CONCORD, N.C.—This is it for Kevin Harvick, a winner of nine races just last year and now on the verge of his earliest career playoff knockout. The steadiest guy in the garage is winless this season—he’s on a 38-race losing streak—and needs a big day at Charlotte Motor Speedway to avoid playoff elimination. Harvick has made it through the second round of the playoffs every year since the elimination format started in 2014, the year he won his only Cup title. Harvick is such a solid bet to be a contender because he’s always in the hunt, always among the leaders, and he’s advanced to the championship round in five of seven seasons. And yet he heads to the Roval at Charlotte on Sunday ranked ninth in the standings, the first driver below the cutline. The field will be trimmed from 12 to eight after this race, and Harvick lags …