Baseball didn't start out as a spectator sport, merely a pastime for children, farm boys, or city folk with enough open park space to play in. Three strikes were the rule and fastballs weren't permitted, to allow rank novices to have a chance at putting the ball in play for some healthful fun and a little light competition. In early variants the pitcher was required to suit the batter's preference as to low or high pitches.
What if we were devising rules made for spectators and played by experienced professionals, though? How about, One Strike And You're Out?
If you put the ball in play, you take your chances on the bases, as now. If the pitcher doesn't throw you a strike, you take first base. If you swing and miss, or otherwise fail to put the ball in play, that's an out. Yes, foul balls are outs - next batter please. Home runs? For the moment I think we can allow them as they are now (fan favorites when not to excess) - but I'm open to every ball out of the field of play being a foul ball and thus an out, if this variant turns out to raise the number of homers versus now by too much.
Same basic design to the game - still 3 bases to run, still 3 outs to retire the side. For the spectator, it goes beyond what the current pitch-clock does to reduce the time between pitches, and eliminates the pitches that don't decide anything - we diehard fans may enjoy the pitcher-batter chess match but the casual fan is usually oblivious and is texting on their phone.
Unsure what constitutes a full game in this fast-paced variant - 9 innings would be over with in under an hour. In early baseball the teams would play to a run total, but I don't think that's wise now. So, 27 innings? (I like powers of 3.) If the games are short enough, complete games come back into the realm of everyday occurrences - is that desirable or not? (One ace pitcher could dominate the league outcome to a greater extent than now.)
There wouldn't be stolen bases (or its variants like hit and run), perforce - are there new and entertaining strategies that could emerge?
The pitcher-batter dynamic would be different, with every pitch essentially a 3-2 offering - no nibbling, no waste pitches or defensive swings. You can still walk a dangerous hitter if that seems strategic, and go after the weaker hitters. Does this version favor the present-day batter, or the pitcher - I mean would batting average and OPS go up or down?
What say you? Better? Worse? Simply "different"? "Too different"?