Here are a few 'brainstorm' ideas to use as a temporary measure until such coding is viable...
1) Any player who is running around the opponent's half, without the ball, can be damaged by defenders eg. 20 points per hit.
2) Players gradually lose health while in the opponent's half, limiting health repair to your own half of the pitch eg. 10 points deduction every 5 seconds.
3) Players gradually lose shot and volley power while in the opponent's half eg. 20% of maximum value every 10 seconds.
The aim behind these proposals (not necessarily with my example values) is to make 'cherry pickers' more vunerable to being fragged, while making them less of an immediate scoring threat, so that they will have to pass to another team-mate who has joined them in attack.
It is quite feasable to use one of those ideas or even combine all 3 options.