When we write difficult surnames, e.g. Novak Djokovic, is it neccessary to use 's in the genitive case? Is it correct to write Novak Djokovic match-ball, or we must write Novak Djokovic's match-ball (that is difficult to pronounce)?
The grammatically correct form would be "Novak Djokovic's match ball." I suppose that the "'s" could potentially be omitted in an effort to save time/space. The only real irregularity that I know of when it comes to the English genitive case is when the word ends in an "s," in which case you can either use the "'s" or just the apostrophe (both are now considered correct- just the apostrophe is almost considered a little old-fashioned though)