The soccer player appeared stale on the field after not playing for a long time.

stale 是形容词，本义指"不新鲜的、陈旧的"，比如 stale bread（不新鲜的面包）。在这里引申为"状态不佳的、缺乏活力的"，形容运动员因久未参赛而表现生疏、缺乏竞技状态。