MJ is particularly harmful to developing adolescent brains. If I were the NFL I'd discourage players from celebrating recreational use.

"The team found that persistent marijuana use was linked to a decline in IQ, even after the researchers controlled for educational differences. The most persistent users — those who reported using the drug in three or more waves of the study — experienced a drop in neuropsychological functioning equivalent to about six IQ points (PNAS, 2012). "That's in the same realm as what you'd see with lead exposure," says Weiss. "It's not a trifle.""

More of the effects on developing brains is detailed by the American Psychological Association article below:

http://www.apa.org/monitor/2015/11/marijuana-brain.aspx