Minimum standard for overcalls
The Blue Book lays out minimum standards for various opening bids but very little about overcalls. Is it OK for a partnership to agree that a 2 level overcall can be a 4-card suit?
At love all, North opened 1H. East then overcalled 2C with:
S: T93
H: K5
D: Q953
C: A432
There were no alerts.
At the end of the hand, North said, "But East only had four clubs."
West then said, "Yes, he does that all the time."
North later asked me if this was OK. I couldn't find anything in the regulations to indicate North was entitled to any claim of damage but if East "regularly" comes in at the two level on this sort of rubbish, many of their opponents are are likely to misinterpret their bidding.
Comments
You are correct that the Blue Book does not require alerts of natural overcalls but it does require "If a partnership has understandings such as opening lighter in third and/or fourth position, responding or overcalling very light or overcalling on four card suits, these should be disclosed on the system card."
This sort of overcall is considered natural (BB 4C1a). However, there are two bases on which a call can be alertable, and I would consider this sort of overcall alertable under BB 4B1b ("is natural but has a potentially unexpected meaning") – if a partnership has an understanding to overcall on four-card suits, then the meaning of their overcalls will be unexpected to many opposing pairs. (There are some unusual overcalling systems, such as Overcall Structure, in which frequent overcalls on four-card suits are expected or even systemically required; if overcalls are made that commonly, then it's quite likely that a pass over an opening bid will also become alertable, because it shows quite a specific hand.)
As a data point, my main partnership plays (1NT), 2!s as "5+ spades, 5-15 HCP". This is undoubtedly natural, but the range is not what most people would expect for a simple overcall in that position, and as such it's probably alertable (and at least one Director has ruled that it has to be alerted). I would think that overcalling on a four-card suit would be substantially less expected than my 2!s overcall, and thus is likely in even more need of alerting.
(As Paul_Gibbons says, a tendency to overcall that short should also be written on the system card.)
4 card natural weak 2 bids are allowed at level 2.
As an interpretation of the announcing/alerting regulations, we regard 4-card 2-bids as sufficiently unexpected that:
My inclination is to ask the pair to alert 2-level overcalls and describe them as, "may be as short as four."
Not sure whether I meant my previous comment here or in the other topic of weak twos.
Standards for overcalls (not just jump overcalls) varies widely. The Blue Book (when it was a different colour) used to cover disclosure of Liverpool-style overcalls (4 card suit, could be <5HCP) - a rear-guard action from David Stevenson and Grattan Endicott to keep these overcalls alive!
If the club has a well-understood minimum standard for weak jump overcalls, and a pair has an agreement which is significantly weaker, then the club/TD can instruct that pair to alert in club events - because the agreement is unexpected. The problem is often is that within a partnership one player's style is standard and the other player's style is significantly weaker - then there may not be an understanding, and proper disclosure is harder to achieve.