in fred and George's last year, malfoy insulted their family, after slytherin lost match against gryffindor.
Fred and George lost their temper, and started bitting malfoy.(only George did that because Fred was hold back)
due to that, Umbridge gave THEM life time ban from quidditch.
for the revenge they gave malfoy a joke shop candy, usually they first test their candies kn themselves before testing them kn others, but this time they decided to test it on malfoy.