Kickback is almost identical to Roman Keycard Blackwood (RKCB), except rather than bidding the traditional 4NT to ask - you instead initiate RKCB by bidding one suit above the trump suit on the 4 level. Easiest will be to show this by way of example, but before proceeding, please check out Blackwood and Roman Key Card Blackwood (RKCB) as it is assumed knowledge.
Example 1
Here 4♣ was a splinter - showing 4 hearts and a singleton club. South decided the hand was suitable and wanted to ask for Aces, and did so by bidding one level above the trump suit on the 4 level which is 4♠, since the trump suit is 4♥.
The slightly tricky part
With RKCB we are used to our responses as they don't change, however with kickback the responses sort of change. For the purposes of this example, lets assume that we play 14/30 RKCB, where the first step is 1 or 4 keycards.
Traditional RKCB structure
After we bid 4NT, RKCB, the responses are
- 1st step (5♣) = 1 or 4
- 2nd step (5♦) = 0 or 3
- 3rd step (5♥) = 2 no queen
- 4th step (5♠) = 2 with queen
You may not have been aware that 5♥ is the third step, because you don't need to be when you play traditional RKCB, but in kickback,
since the asking bid moves, the responses also move
So, lets continue the auction that we started earlier
Example 2
Here partner has shown the 1st step, by bidding 4NT. Which shows 1 or 4 keycards, but contrast that with this diamond suit auction, lets for the sake of simplicity change the hand and auction ever so slightly.
Example 3
This auction (strikingly similar to the previous example except this time in diamonds), partner has splintered. You decide to bid RKCB, which is 1 bid above the trump suit, on the 4 level, 4♥. Or put differently, the bid of 4♥ is RKCB since it is one suit above the trump suit, on the 4 level.
Back to the slightly tricky part
After we bid RKCB, we have to stop for a moment to think how many partner is showing. It takes a bit of practice. My favourite hack for doing it is this, but others do it differently
My method
I remember the responses to traditional RKCB. If, like in example 1, RKCB is bid by bidding 4♠, I know its 1 level lower than 4NT. I think of it like this "all the responses are the same as normal RKCB except they are 1 level lower than they normally are, since my asking bid was 1 level lower".
So, for example, 5♥ response is actually the real 5♠, which is 2 with the queen.
If that doesn't work for you, it is just about figuring out what does, just simply practicing it a few times will help you find your groove.
Advantages
The key advantage is that it keeps the bidding lower when you bid RKCB so you can more conveniently sign off if partner doesn't have the number of keycards you hoped for. It also gives you more room to ask for the Queen, while keeping open the possibility of signing off on the 5 level.
For advanced/expert pairs, you also have the bid of 4NT now freed up which can be used for other things, since it is no longer the way to bid RKCB.
Disadvantages
The main disadvantage is that you lose a natural cue bid on the 4 level. People that don't play kickback can use the kickback bid as a natural cue showing control and strength. So, if for example you have a hand where you are not certain of slam, but you want to tell partner that you have a good hand, you might have one less cue bid available
My recommendation
I personally prefer not to use kickback and only suggest using it if you feel comfortable and/or enjoy using it. It is not something that is essential at all for taking your bridge to the next level. General bidding judgment and partnership judgment will sometimes avoid the situations where you bid RKCB and are stuck after partner responds. You should try to not expect more than is realistic - for example you shouldn't typically bid RKCB with 0 or 1 Ace only, its unrealistic to expect partner with 3. Or, your partner shouldn't over inflate their hand, for example by showing a very good hand despite not having any keycards!
Read next: Blackwood and Roman Key Card Blackwood (RKCB) · Best slam bidding conventions · Cue bidding: Slam bidding made simple