This from Welles'interview with Cahiers in '65.
"My relationship with Heminway has always been very droll. The first time we met was when I had been called to read the narrartion for a film that he and Joris Ivens had made about the war in spain; it was called Spanish Earth. Arriving, I came upon Heminway, who was in the process of drinking a bottle of whiskey; I had been handed a set of lines that were too long, dull, had nothing to do with his style, which is always so concise and so economical. There were lines as pompous and complicated as this: 'Here are the faces of men who are close to death",'and this was to be read at a moment when one saw faces on the screen that were so much more eloquent. I said to him, 'Mr. Hemingway, it would be better if one saw the faces all alone, without commentary.'
this didn't please him at all, and since I had, a short time before, just directed the Mercury Theatre, which was a sort of avant-garde theatre, he thought I was some kind of faggot and said, "You---effeminate boys of the theatre, what do you know about real war?"
Taking the bull by the horns, I began to make effeminate gestures and I said to him, "Mister Hemingway, how strong you are and big you are!" That enraged him and he picked up a chair; I picked up another, and right there, in front of the images of the Spanish Civil War as they marched across the screen, we had a terrible scuffle. It was something marvelous: two guys like us in front of theses images representing people in the act of struggling and dying... we ended by giving each other accolades and drinking a bottle of whiskey. We spent our lives having long periods of friendship and others during which we barely spoke. I have never been able to avoid gently making fun of him, and this no one ever did- everyone treated him with the greatest respect."
I would love too have been there, but I doubt it ever happened. I certainly have never read any other account of this event. Besides, wasn't Orson more into throwing Hot Plates, than swinging theatre chairs? Still says much about his feeelings for Heminway, though.