A 14th-century squire (Heath Ledger) fulfills his life’s ambition by posing as a knight and achieving stardom on the European jousting circuit. Writer/director Brian Helgeland’s film gets off to an appealing start, blithely anachronistic and playfully reveling in a thumping rock score from the 1970s and ‘80s. But what begins as Monty Python and the Holy Grail loses its comic chops midway through and tries to morph into Rocky, with a run-of-the-mill triumph of the little guy with a big dream. Helgeland begins well (it’s easy to inspire good will when you open with Queen’s evocative “We Will Rock You,” with some graceful moments in the first half (such as a banquet dance to David Bowie’s “Golden Years”). But he’s a one-track director who can’t blend drama with comedy, much less irony.