Maybe some more specificity would help you get some answers: what time period? Pirates today are probably bad with swords, for example. What area? Pirates in the South Pacific wouldn't carry the same equipment as those in the North Atlantic. What do you mean by "average"?

To answer this, the first thing that needs to be addressed is your mention of how pirates are portrayed in film. The way pirates are portrayed in film, with grand adventure and bombastic, swashbuckling sword fights, is not a very accurate depiction of pirates during the Golden Age, but more of a romanticized portrayal.

The truth is, being a pirate in the Golden Age was filled with a lot of downtime, and when they did find a ship to plunder, normally there wouldn't be any casualties on either side.

Pirates typically used schooners or sloops, which were very light, but very fast vessels. Unless they were led by a skilled captain, they weren't going to be winning any battles against something like a Man-of-War (Stede Bonnet being a prime example of that). However, they could swiftly sail close to poorly armed merchant ships and board them before they could attempt an escape.

Once boarded, most crews would give up whatever goods they had, and the pirates would let them go on their way once all of the plunder had been acquired. There were of course instances where pirates were met with resistance, but that was an exception to the rule.

Because of this, it's actually quite hard to find a substantial amount of documentation on how skilled pirates were as sword fighters. However, there is at least one famous documented skirmish involving pirates that could be seen as reminiscent to the swashbuckling action of a pirate movie, and that would be the Battle of Ocracoke Inlet between Blackbeard and Lt. Robert Maynard of the British Royal Navy

The Battle of Ocracoke Inlet is the only recorded instance of Blackbeard ever engaging in a sword fight. While I can't find anything on the quality of swordplay from his crewmen, Robert E. Lee's Blackbeard The Pirate, A Reappraisal of His Life and Times documents the battle as so.

Blackbeard waded into the melee, swinging his great cutlass. It was a wild windmill attack that no one in front of him could repel with a blade. He had to be stopped by a pistol shot or by someone from the rear. Both methods were tried. Blackbeard from time to time supplemented his blade swinging with a pistol snatched from the bandolier of pistols across his chest. These were single-shot pistols, thrown aside after being used.

An heroic touch was given to the battle by the ferocious confrontation of Maynard and Blackbeard—the champion of law and order and the champion of piracy—face to face. In this epic struggle, one or the other had to be annihilated. When they met, each pulled a pistol and fired. Blackbeard was being rushed at the time from all sides, and his shot missed its target. But the shot discharged by Maynard plowed through the great body of Blackbeard. It failed to halt him, however; he fought on with fury.

In the heat of combat they engaged each other with swords. A powerful blow of Blackbeard's cutlass snapped off Maynard's sword blade near its hilt. A blow of such terrific force would ordinarily have knocked the sword flying, but apparently Maynard was holding it with a frenzied grasp. Hurling the hilt at his adversary, Maynard stepped back to cock his pistol and at the same instant Blackbeard moved in for the finishing blow with his cutlass. But at the moment in which he swung his cutlass aloft, a British seaman approached Blackbeard from the rear and gave him a "terrific wound in the neck and throat." The cutlass, raised for the finishing blow, swerved as it came down merely grazing the knuckles of Maynard, cutting them slightly.

It may also be worth noting that Blackbeard did serve as a seamen for the British Royal Navy during Queen Anne's War, and would've been trained in gunnery and swordsmanship. Whether or not many other pirates in the Golden Age came from a similar background is a subject that is up for debate, as very little is known about the backgrounds of even the most well documented pirates.

The buccaneers of the Caribbean in the 17th century were excellent marksman.

They began as a multi-national community of mainly English, Dutch and French ex-seamen who were dissatisfied with the tyrannical nature and terrible working conditions of navy ships or merchant vessels. They found a lucrative business as hunters of the wild boars that inhabited the land. The buccaneers would sell hides, meat and tallow in exchange for hunting tools, musket rifles, gunpowder and shot, and general provisions. The name ‘buccaneer’ actually comes from this practice. The hunted meat when cured was called boucan. The hunters were then called Boucaniers by the French, which led to the English calling them Buccaneers. They were mainly concentrated around the Northwest of Hispaniola, now Haiti, and the islands surrounding it such as Tortuga.

While they sometimes hunted passing trading vessels when there was a lack of optimal hunting or bad weather, it was not their primary livelihood. This changed in the 1630’s when the Spanish in Santa Domingo felt threatened by the ever-increasing poaching practices of the buccaneers and led a systematic slaughter of the cattle and wild swine that the buccaneers hunted. This completely backfired however as the livelihood of the buccaneers suddenly vanished and the only other option they had was to resort to piracy. Throughout the 1630’s there was increased Spanish aggression against the buccaneers. This culminated in a massive offensive in 1638 where the Spaniards attacked the buccaneers safe haven’t of Tortuga. The Spanish slaughtered many buccaneers and burnt down as many buildings and plantations as they could but the buccaneers survived and.

I'm not too sure on their swordsmanship but they were incredible marksmen.

J. G. Marx, “Brethren of the Coast”, in D. Cordingly(ed), Pirates: terror on the high seas, from the Caribbean to the South China Sea, (East Bridgewater, 1998)

J. Burney, History of the Buccaneers of America, (New York, 1907)

D. Mitchell, Pirates, (New York, 1976)