I don’t mean to make light of you question which is a good one, but the easiest way to defend against aggressive base running, is to cut down on the runners reaching base. There’s absolutely nothing you can do about hits because they’re gonna happen no matter what ya do. But, you can do something about runners who ROE or reach on walks or get HBP. If you cut down on just 1 walk or HBP and 1 ROE per game, that’s 2 runners who never get the chance to advance.
Originally Posted by The Flush
As for how kids that age in a rec league would defend against aggressive base running, they really can’t. Its because it’s a lot easier for one kid to run 60’ in a straight line, than it is for a pitcher to make a good pitch the catcher can handle easily, the catcher to catch the ball then execute all the muscle movements correctly to transfer the ball and make a good throw to a base, then have the fielder receiving the throw get into proper position to catch it, catch it, then apply a tag without losing control of the ball.
Until the distance between bases get longer and the players get more skilled, you can only keep trying to teach the fielders the skills they need to execute correctly in order to catch runners.
The pitcher who’s afraid to throw strikes, will soon be standing in the shower with the hitter who's afraid to swing.