Student or Learner
My father took real pride in what the band were doing. But he also really enjoyed sticking the boot in, just because he could, with a snigger.
Does it mean that although he was proud of the band he liked to interfere with the band and laughed at them.
Sticking the boot in is being very critical in a nasty, rather than a constructive, way.
This man appears to feel superior to the band and seems to be in a position to influence what they do. By sticking the boot in with a snigger, he's trying to emphasise his superiority by laughing at their efforts while not providing much help.
buggles(not a teacher)