the team u are talking about looks like he is what is called a day trader. except instead of buying younger players he buys veteran players and then sells them a few weeks later. If you have the time this can be very profitable, but you can quickly go into debt.
It looks like he's holding on to most of the players two months or so, and the "profit" is extremely small in almost every case even before figuring in the wages. It seems more like a guy who just turns over his players more frequently than a day trader.