So the rules for Reverses are:
1. Bidding Sequence - A Reverse is:
a. A non-jump bid;
b. Made on opener’s first rebid (even in competition);
c. Made at the 2-level;
d. Made when responder responded at the 1-level (Reverses are off if responder responded at the 2-level); and
e. Made in a new suit (not NT and not a suit already bid by opener or responder) that is higher than the suit opener opened at the 1-level.
2. Strength – A Reverse shows 16-21 HCP if only 5-4. For each extra card in length, opener may have one fewer HCP. ( e.g. With 6-4 distribution, opener may have only 15 HCP.)
3. Length – The suit opened at the 1-level must be longer than the suit rebid by opener at the 2-level.
4. Distribution – The reverse is usually an unbalanced hand (contains a singleton or void) or else opener likely would have opened 1NT with 16 or 17, rebid 2NT with 18 or 19, or opened 2NT with 20 or 21. Occasionally, opener can have 2-2-4-5 distribution where opener opts to reverse rather than bid NT due to worries about stoppers in one or both of the doubletons.