I had missed this one when Flagstaff Films first posted it to Twitter last month, but in viewing it, I noticed a Cubs pitcher was involved, so that got me to put my sleuthing cap on:
The single clue 1963 made this one actually pretty simple. It’s not easy to read the number on the Cubs pitcher’s uniform, but the Mets hitter is wearing No. 11. That’s Duke Snider, who played just that one year for the Mets. Snider also wore No. 4, his old Dodgers number, for the ‘63 Mets, but he’s the only player who wore No.