I think it’s mainly to put pressure on the batsman, Dave, to hopefully restrict his shots, plus occasionally there will be some small ricochet off his bat that doesn’t travel that far - with a fielder in that close there’s a very good chance they’ll take that catch. I hated the position, was always a bit nervous there, but the captain says field there, you field there. Of course, very often as soon as the batsman is clearly lining up to play an aggressive shot, the fielder there tends to look or turn away anyway. And in answer to your question as to whether the batsman can swing away, the plain answer is yep! Some batsmen will decide the best form of defence is attack and make a point of playing aggressively in the hope of driving any of those very close fielders away. Mate of mine, superb batsman, hit a ball once with some considerable venom to the “leg” side (basically directly to the batsman’s left) and hit the “short leg” fielder square in the face (“short” is another term for fielding so close, would shortstop be the same?) This is a very hard cricket ball at pace and at, effectively, point blank range. We all thought he’d killed the guy. Seriously, he went down like he’d been shot and it looked awful bad. Fortunately, he was “ok”, but his nose had been obliterated and off to hospital he went, leaking claret everywhere (on the playing area too, how inconsiderate of him ) Nobody fielded that close to my teammate again that afternoon.