In ‘lock ‘em up’, the batting team earn ‘upgrades’ (more open spaces to hit the ball into) by ‘locking’ fielders into disadvantageous fielding positions by successfully hitting the ball into designated target areas.
It is, in many respects, a gamified version of the old ‘Lord’s game’. I have played it only with a front foot drive, but I can see no reason not to adapt it to for other attacking strokes.
This game has developed from an idea shared by @imsporticus , modified to include concepts from @davidhinchliffe and @ianren21 — thanks to all of my fellow coaches for the inspiration, and also to @AmyPrice_10 et al. for the theoretical underpinnings of sports coaching informed by digital game design.