It is forbidden to block the ball by jamming it with the feet, legs, etc., if this prevents an opponent from playing the ball (in accordance with the rules). The addition of the rule conformity is important, because it is a variant of dangerous play.
For a more values-based interpretation - players have to keep the ball 'in play' in a way that the other team can interact with, without posing a danger to the player(s) on your team.
As in this case the play is either unstoppable, or requires the other team to somehow extract the ball from between two players' chests, it's a fun theoretical loophole - but is not a fun or safe way of playing football if it became a commonplace strategy. In most cases, this would be seen as daring dangerous play - either the other team needs to kick it free, or jostle the players until they drop the ball, both of which are taking pretty significant risks of injury.
I mean... outside of breaking the basic concept of sportsmanship, apparently there are rules about keeping the ball free?
Someone else commented the rules, and I suspect English isn't their first language, so I didn't pick up an absolute answer in my lazy browsing, but they came with receipts.
Even if completely stopping the ball from moving was not a violation:
The outside circle cannot actually prevent opponents from getting to the ball, that's obstruction. You can't set a screen in football while ignoring the ball.
So you have two players forced to move in an awkward way. The defenders are just going to push them off the ball with a shoulder to shoulder push.
Someone did this once hundreds of years ago and the coach screams "Just knock them over! Grab them and throw them down! Tackle them!" and all at once American Football was born.