I think we have a few issues with the distance between us at the moment, I've mentioned a few times that my character is utilizing the full length of his spear, roughly six feet, and staying about that distance away from your character. Considering his step back as well, it seems unlikely that your character would close to within arm's reach with a single step.
Also, it's less of an issue, but you didn't really clarify how your character was sweeping away Brennus' spear, if he was doing it backhanded (knocking the spear off his left side) or with a more comfortable strike that would place the spear at his right side (and potentially leave it as a major danger to his un-shielded flank.)
Ultimately, your character is not going to be able to step close enough to carry out the move you said, unless you intend to pursue Brennus and take around two steps forward. (or whatever becomes necessary depending on my actions, and this is assuming Brennus -can- be caught, which is about 50-50 in my opinion.)
Now, I don't like to tell people what to do, but I'd recommend just using the long pointy object your carrying to make up the added distance instead.