The Ukrainian goal that wasn't awarded is being held up as evidence that UEFA's preferred 5 official solution should be shelved in place of the goal-line technology already favoured by FIFA. How could the extra official miss the fact that the ball had wholly crossed the line? Perhaps he was distracted by John Terry's balletic manoeuvre, fearing/hoping he might do himself an injury.
What this highlights is that the officials, including the one in the middle, aren't certain what is going on most of the time. The pace of the game is so fast that an involuntary blink of the eye, or being 6 inches out of optimum position, can be enough to miss a crucial moment. Even when you see something, the limited time and angle can cause you to misinterpret it. You are never, ever going to be as authoritative as Andy Townsend, which is a sobering thought. (That said, at least you won't make as many mistakes as Clive Tyldesley: "it's all square in the other match, where Sweden lead France by a goal to nil").
What TV viewers often forget, as a player dramatically hurls himself to the ground, is that this does not appear so obviously staged when viewed in real-time and at a distance. It's routine for a live spectator to say "I'd like to see that again on Match of the Day" when a penalty is given or denied. Players emphasise fouls because they fear the officials will otherwise miss them. It's like Kabuki, a form of gestural theatre, where actions must speak louder than words.
The consequence is that referees and their assistants rely on a mixture of hunches and probabilistic logic to make key decisions. In recent years I've occasionally run the line for my son's team. Despite being an experienced (if limited) player and spectator, trying to spot offside even with the sedate pace of half-interested boys on a cold day is a challenge. Mentally flipping a coin is not unknown.
Inevitably, this leads to drawing inferences from a player's prior behaviour during a game, so lots of early diving usually gets its "reward" when a legitimate penalty is denied. It can also lead to subconscious expectations based on reputation, notably with card-magnets like Joey Barton. This in turn can be biased by prejudice, as players are assumed to exhibit national characteristics. Thus in the coming quarter-final clash, England's players will be watched for over-zealous, scything tackles, while Italy will be watched for shirt-tugging and sneaky ankle-taps.
Once goal-line technology is introduced, it's hard to see the line being drawn there. The ability to check on a replay whether a foul was inside or outside the penalty area would be an obvious next step. Ultimately, the demand for better refereeing won't go away until they become robots, perhaps androids modelled on Pierluigi Collina.
As England fans are suddenly getting excited (the "footballing gods are smiling", according to Adrian Chiles), you can expect the next game to be a disaster. I'm going for 1-1 at full-time and Ashley Young to miss the crucial penalty.