“Look at the balance on it! If the Nimbus series has a fault, it's a slight list to the tail end — you often find they develop a drag after a few years. They've updated the handle too, a bit slimmer than the Cleansweeps, reminds me of the old Silver Arrows — a pity they've stopped making them. I learned to fly on one, and a very fine old broom it was too…”
I'm not sure what "a drag" is supposed to mean here. The context is talking about the broomsticks they flew on. I've looked up the word 'drag' in dictionaries, but I don't know which one is fit for the context.