1st post.
Couple of significant points, one its customary in most fights for each person to introduce their own character, though you can definitely set the scene its best not to set anything in stone for your opponent, in the fashion that you removed Brennus’ shield, etc.
If we’d agreed beforehand that we were fighting with wooden swords, then the only additional thing I would recommend was stating if they weren’t average sized longswords, as the size difference counted against you later on.
In a more standard arena fight the introduction post should usually include – your character’s full list of attire, equipment and weaponry. Anything you don’t mention in your intro post is technically not allowed to be used, regardless of if it’s in your sheet (save for magical powers and the like, this tends to only apply to physical items.) 

2nd post
You said ‘his sword, in his right hand’ this led to the later misunderstanding that he was wielding it one handed, have to be careful to specify how you hold your weapons, etc.

3rd post
Forgot to specify how and with what hand your character attempted to grapple, nor your target (unless sword hand always means dominant hand, but I’d still say that is a little obscure and can be misconstrued.) If I wanted to, I could specify for you in my next post, having you commit to a grapple with your right hand for example (which you probably would considering the situation) which would weaken your block (the most important aspect of your defence.)

Other than that, all cool. I think your counter would probably have worked if my character had over-stretched himself a little bit further. In future you may want to specify you’re looking for sword duels, as your character will be at a major disadvantage fighting Brennus with his full equipment for example.

Hope this helps, have fun in the Arena.