As of Blood Bowl v6, certain teams have been classified as "Advanced Teams" perhaps not suited to beginner players due to their more challenging player selection, confusing special rules, or perhaps other, less tangible factors.
The following teams are currently rated officially as "Advanced" by the BBRC. Not everyone agrees with these ratings, and indeed, some long time Blood Bowl players would suggest that other teams should be added to this list, or removed from it. That said, beginning players should be advised that these teams might not be as easily playable "out of the box" as the other races available.
Occasionally, Leagues will offer a bonus to players willing to coach an Advanced Team, but this is not a universal practice at present.
"Advanced" Teams according to Blood Bowl Competition Rules v6
The teams from the New Teams for Bloodbowl document have not been officially evaluated as yet. However, some players have suggested that at least two (2) of the new teams should be added to this list. Note that this is completely unofficial, however.