The company decided to replace the sales manager due to the underperforming results.

underperforming 是动词 underperform 的现在分词形式。underperform 由前缀 under-（表示"低于、不足"）和动词 perform（表现、执行）组成，意思是"表现低于预期标准"。 underperforming results 指的是"业绩表现不佳的结果"。