Question about players numbers

[Clark Kent]

Randy Moss is obviously a raider and has chosen the #18. Is there (or was there) a rule against this or something? Just recently over the last few years there’s been a lot of guys choosing numbers (WR for example) like 19, 11, 18, etc...

Just wondering...

 

[Nublar7]

Last year was the first year that WRs were allowed to start wearing numbers in the teens. A lot of players are now taking advantage of it.

 

[Clark Kent]

Last year was the first year that WRs were allowed to start wearing numbers in the teens. A lot of players are now taking advantage of it.

What about Keyshawn? He's worn 19 since he was a rookie.