How many?

[Sheffields Finest]

If keepers can't come off their line, surely outfield players can't come in the box either without sanction either??

 

[Peter Grove]

The IFAB apparently doesn't think so. I'm not saying I agree with the following but here is their view on it, taken from the FAQ on their website:

Q4: Why is it not a caution (YC) for players who encroach early?
If the kicker or goalkeeper infringes the Law their illegal action can directly can directly affect the outcome of the penalty kick but encroachment does not directly affect the outcome of the penalty kick so is not as serious.