Are you sure you aren't thinking of 'wide receiver', because first receiver doesn't make much sense in an American Football context, as 99 times out of 100 there is no second receiver. It does in rugby though, in the back line typically the fly half is the first receiver, inside centre is the second and so on.
There is an ongoing thread on the rugby forum talking mentioning Ronan O Gara's analysis and how he uses 'insider' terms that a layperson wouldn't be familiar with it (-1 and -2 defender was the quote) and I wouldn't be surprised if first receiver actually is a rugby term
I cannot remember the context of "rookie" comment but it was All Ireland final Dublin/Mayo i think but not sure, i just watch big games.
I am familar with term wide-receiver but did not hear it here in relation to our daily sport...
For me all of the Ronan terms are perfectly understand and my point i would rather fallow Ronan than what i heard recently.
I am very much in the minority here so i will adapt pretty easy or switch off...