His homework was sloppier than last time, with handwriting almost illegible.

sloppier 是形容词 sloppy 的比较级形式。sloppy 意思是"马虎的、潦草的"，由 slop（泼洒、弄脏）加后缀 -y 构成，形容像被泼洒过一样不整洁的状态。sloppier 表示"更加潦草的"。