Many critics wrote off the film, but it became a surprise hit.

wrote 是动词 write 的过去式，意思是"写"。 off 在这里与 write 搭配使用，表示"取消、放弃、认为...失败"的意思。 wrote off 是一个短语动词，意思是"不看好、认为...会失败"，常用来表示对某人或某事的负面评价或预测。