Another thing【主语】// that Messi does quite often, and (he does it省略)quite well if I may add【后置定语】//, is 【系动词】//building the confidence back up for those players enduring a rough patch【表语】.
参考译文:梅西经常做的,而且如果我可以补充说的话,他还可做得相当好的另外一件事情,就是为那些经历艰难时期的球员建立信心支持。
备注(1):句子整体框架结构:Another thing is building the confidence back up for ...
备注(2):building the confidence back up for为动名词作表语。来陈述主语(另外一件事)具体内容。
备注(3):enduring a rough patch为现在分词作后置定语修饰前面名词“players”。