After two years without playing soccer, his skills became noticeably rustier.

rustier 是形容词 rusty 的比较级形式。rusty 由名词 rust（铁锈）加上后缀 -y 构成，本义是"生锈的"，引申为"生疏的、不熟练的"，指因长期不练习而技能退步的状态。rustier 表示"更加生疏"。