The fight is indeed a bit difficult to follow, partly because they didn't establish the characters' positions clearly. The way I interpret it is Guts manoeuvring around Zodd by using the force of the second attack to propel him toward Griffith's direction, using the momentum from Zodd's blocked...
Long time lurker, I registered years ago but never posted since I enjoyed reading the insightful discussions that took place over the years within this forum. I was shocked and saddened by the news like everyone and struggled to process it. I wished that there was a mistake or a misunderstanding...