If Oliver Queen is a master swordsman, why doesn't the Green Arrow carry a sword? Wouldn't it come in handy for all of those fistfights he loses?
It's not unknown for Green Arrow in the comics to carry a sword.
From the Wikia
In a flashback sequence encompassing issues 66-68 (while he was recovering from said injuries on an island), he hired some of the best martial arts instructors in the world to come and train him and his companions.
While initially an inferior fighter and prominent non-martial artist, in recent continuity he has trained to become a proficient martial artist in several forms of hand-to-hand combat including judo, kickboxing and karate, although not on a level with Black Canary. He is proficient with a sword, as evidenced by a battle with Deathstroke in issue #62 and by a battle with Red Hood in issue #71
Obviously in the TV series he's shown as having then necessary skills to defeat well-trained swordsman but it's not his primary skill and his unarmed combat skills seem more than adequate.
Would a sword be useful, undoubtedly, but he got quite a lot to carry around already.
It's also, arguably, worth stating that Oliver has tried to desist from killing enemies in recent times and using a sword on someone while not necesarily lethal does do a fair amount more damage than a well placed punch.
I suspect that the producers writers want to keep the emphasis on his archery skills. The show is called Arrow after all.
Oh, and this is so much better than a boxing glove sword.