Modern fencing and historical fencing are different beasts. The sword weight is different. The sword length is different. The weapon class is different. Everything is different, including the vectors of attack and the possibility of death. Now, to be fair, someone who went from historical (HEMA) fencing into a sudden life or death duel with a historical personage would also be screwed. They’d be slightly less screwed, but still screwed. The same is pretty much true when you put most sports martial artists up against cops or professional soldiers. They’re not trained for it.
Modern fencing has moved in the direction that is beneficial to itself as a sport rather than as a form of combat. There are a great many techniques performed by fencers that are excellent in competition but would get you killed (or at least a double suicide) in a live bout with live weapons.
This is true of any type of sport martial art. When you remove death from the equation, people have the opportunity to be more reckless and, in some ways, more creative than they would be if there was a chance of actual impalement on an enemy’s blade.
The real problem for this character though is going to be the blade weight. Even if they’re just shifting to a historical epee from a modern one, they’re going to pick up a few pounds. Given no time to adjust, that additional weight will hamper everything from speed to accuracy to their endurance. The time they waste adjusting to blade weight is time their enemy has to break their defenses and stab them. They will face similar difficult with the historical sabre. That’s if they’re lucky enough to hit a historical period with a blade they recognize. They won’t know what to do with the rapier, or any of the other swords.
There are also three types of modern fencing blades that each have their own associated rule set. This could be a problem for them.
Fencing Rules for the Novice Parent has a good breakdown, but I’ll list the basics here.
The Foil – thrusting only, hits only count when struck with the tip of the blade. Striking is limited to the torso, but covers the groin, neck, and back.
The Epee – the epee like the historical epee is a dueling sword, strikes include the whole body. Thrusting weapon, scored only with the tip.
The Sabre – the traditional sabre is a military/cavalry weapon, it is curved. It’s a cutting and thrusting weapon, and the entire upper body is an available target. So, this includes the arms.
It’s worth noting that “cut” and “thrust” with modern fencing weapons mean which part of the blade touches the opponent’s body. It is possible to be hurt with a modern fencing blade when not wearing protective gear, but it’s nowhere near as dangerous as the historical swords.
You don’t have to take my word for the differences though. Here’s Matt Easton talking about the differences between sport fencing and historical fencing. He refers to it as a game of “electrified tag”. Modern fencing isn’t about swordsmanship in a classic sense, it’s about scoring points and getting around the (rather restrictive) rules.
This doesn’t mean the sport doesn’t have value, it does. It’s an incredible form of exercise, show of athleticism, developing incredible reaction speed and timing. It’s great for your brain. It isn’t combat. It doesn’t prepare you for combat.
However, assuming they survive, those ancillary skills they mastered in sport fencing can be re-applied to a study of historical fencing. They go into this story athletic, quick thinking, strategic, creative, and with reaction times that are well above average. Sport fencers are fast on their feet.
There’s some good maneuvering that can be done with this character on a story level, but their skill set isn’t on a 1 to 1 parity with a practiced swordsman straight out of history.