Say one of your friends wants to borrow one of your cards for a while, and you let them use it. The said card will then be sent to the trade pile. In the trade pile, the card will have a 'transfer' option, and when you hit transfer, a list of your friends will pop up and you select the friend you want to send it to. Also, the amount of games left on the players' contract will only go down with the games your friend has played with it for example: Say Jordan Eberle is the card your friend wants to use, and his contract has 90 games left. Say your friend plays 10 games with that card. So when you get the card back, instead of the contract being at 80 games left, it is back at 90. And all your friend has to do to give you the card back when he/she's done, the card will have a 'return to friend' option, and the card will end up back in your trade pile.
Hope that was easy to read.
Makes sense to me.
Also when lending a card to a friend, you should have an option to give him a "contract" of say 10 games, then after those games are played he is automatically returned.