But because we don't know what is going to happen, referees have to keep focussed for 100% of the match. One little slip in concentration could mean they miss a little touch on the ball by the attacker and give a corner instead of a goal kick, it could mean they miss a handball claim, or even if the ball crossed the line or not.
I know I've lost concentration during some of my matches, as an Assistant Referee I gave a goal kick instead of a throw in! I knew the ball had gone out off the attacker, but instead of flagging for a throw I just pointed for a goal kick. In my defence, the playing conditions were atrocious and the match should never have been played, so it was a relief when the referee abandoned play a couple of minutes later.
An incident in the Turkish Super Lig inspired me to write this.
During a match between Kasimpasa and Besiktas, a second ball entered the pitch from the crowd. Play continued as normal, so the referee didn't stop play, but the Kasimpasa defender Ryan Donk picked the ball up and ran back as Besiktas came forward. What happened next would be worthy of a slot on a Question of Sport. He threw the second ball at the match ball in the penalty area, causing the attacker to stop play. The referee cautioned Donk, and should have restarted play with a penalty to Besiktas. (I'm not 100% certain that he did though.)
If I had my way, I probably would have sent him off (although this wouldn't have been the right decision in Law) as it is down right cheating, and as with diving (simulation) should be punished accordingly.