Why Does the NFL Have a 40-Second Play clock?

In theory...

sec-urity

OK OK, you minused it out of me!!! It's because we don't use the metric system... that's why!

always glad to be a small part in making the world a better, more sarcastic place to live!

Or it is because everyone is so dumb that no one could understand the coach unless there was a 40 second play clock

I agree entirely!

The running game is only used to run the clock down. Since they will only be able to run down 62.5% of the time they would normally be able to run down, it would become 37.5% less effective. Not many teams set out at the start of the game to run more times than they pass in a game.

It makes sense. A pass is the most immediate way to score. It probably is 50-50ish until about 3 minutes to go in a half, when pretty much every down is a pass. Because they are passing, that could be an extra 10 "passes". Whilst they may not set out to run, if a few runs are more successful, then you obviously turn to the run more often. Passing is generally the Number 1 option. Running is Number 2. Hence a QB tends to be more important than an RB. Usually. A few break this rule. Miami Dolphins when they had Ricky Williams in 2004, e.g.