A career in professional sports was ruled out early in his life due to an injury.

ruled 是动词 rule 的过去式，rule 本意是"统治、支配"，在这里引申为"决定"。 out 是副词，表示"在外、排除"的意思。 ruled out 是一个固定短语，意思是"排除、否决"，表示某事被排除在考虑范围之外。