You probably remember the film A Knight's Tale (2001) even if you didn't see it. There's that memorable scene where knights joust to the tune of Queen's "We Will Rock You". That made it into the previews. What's anachronistic isn't the soundtrack so much (not enough medieval music survives from specific periods and areas to provide one), but the fact that the audience at the joust is beating in time on the railings and singing along with the words-in mid-14th century England.
There's a method to the madness. The movie does attempt to get across how medieval people felt about their sports-specifically, jousting-by showing some similarities between medieval and modern sports audiences. And the addition of a highly sarcastic Geoffrey Chaucer (Paul Bettany) into the mix as part of the peasant Hero's fan club/cheering section/tutor in acting like a knight is lots of fun. Rufus Sewell as the snobbish villain and James Purefoy as Edward the Black Prince of Wales add pedigree. Purefoy especially gets across how disturbingly quiet and deadly a medieval knight could be-and how scary your average medieval person could find the son of a king.
It's a shame, though, that Chaucer (this week's book review subject) and Edward's ages don't match up with the story. Also, Purefoy has short hair and is cleanshaven, while the images that survive of the Black Prince show him with long hair and a beard. Nor was he called "The Black Prince" until centuries after his death. Most disappointing, Edward was notorious for his contempt toward his social inferiors-murderously so toward French peasants. So, the major epiphany that occurs between him and the Hero (played by a buff Heath Ledger) would never have happened.
Also, while the heroine, Lady Jocelyn (Shannyn Sossamon), is sparky in a goth (modern not early medieval) sort of way, she ultimately exists just to be the prize in the conflict between the Hero and the Villain and part of the Hero's cheering section. A female sidekick, Kate the Farrier (Laura Fraser), is similarly wasted. Further, not enough thought goes into the mix of medieval and modern and some parts...well, they drag. So, the film is ultimately very uneven.
That said, if you like Heath Ledger, you've already seen the superior Casanova and you're looking for a little medieval fun, check out A Knight's Tale.