Whenever the teacher asked a question, he would sidestrack with jokes.

sidestrack 是由 side（旁边）和 track（轨道）组成的复合动词，字面意思是"从主轨道转向旁边"，引申为"转移话题"或"避开重点"。在句中表示用玩笑话故意偏离原本的问题。