Last night, Uruguay were playing Ghana in the World Cup. In the last minute of extra time, the score was 1-1, and Ghana had a very good shot on goal. The Uruguayan striker Suarez quite clearly pushed the ball off the line using his hands. He was sent off; Ghana missed the resulting penalty; Uruguan went on to win on penalties.
The problem is this: As the rules stand, Suarez's action was sensible and was self-sacrificially doing the best thing for his team. Had he not handled the ball off the line, his team would have been knocked out. As it was, handling the ball off the line ensured that his team still had a chance of going through, a chance which they duly took. The rules therefore encourage fouls in such situations.
The most obvious modification to deal with this would be the introduction of a penalty goal, as in Rugby. The rule would run something like this:
If a player commits a foul to prevent an otherwise certain goal, they shall be sent off and the referee shall award a goal to the side and player that would have scored had the foul not been committed.