Translation:My older brother plays basketball pretty well.
This seems to be explained in Chinese Grammar Wiki's Degree Complements article: https://resources.allsetlearning.com/chinese/grammar/Degree_complement#Degree_Complements_with_Objects.
Based on the article, this is a "degree complement with [an] object" where "得不錯" is the degree complement and "籃球" is the object. Since both must be adjacent to the verb ("打"), one must copy the verb to get what is literally, "My older brother plays basketball, plays well.
It also looks like "打" is a special verb that "verbifies" a noun, so "打籃球" (to play basketball) is literally "to basketball" while "打電話" (to call) is literally "to telephone".