ArcticInferno said:
Why do you stand on 9/9 against 7, but split against 8 or 9, and then stand for 10 or A.
The pattern doesn't make sense.
According to "Blackjack Bluebook II" page 62, a hard 18 will beat a dealer's 9 only eight out of twenty.
According to the book, two 9's against a dealer's 9 is better than one 18 against 9.
I'm assuming that the explanation is similar for an 18 against a dealer's 8.
What about an 18 against a 10 or an Ace?
I would think that the dealer's 10 or Ace is stronger than a 9, so if you have to split 9/9 against a 9,
then you should certainly split 9/9 against 10 or Ace.
What about an 18 against 7? That makes even less sense.
You stand on 9,9 against a 10 or an Ace because you are the underdog whether you split or not. If you do split you are likely to be making 2 losing hands out of one. Even if you hit each 9 with a 10 you're only slightly improving your hand and will not beat a dealer 20. It's simply not worth the risk.
You split 9,9 against a dealer 9 because you have 18 and the dealer is looking at having 19. You're the underdog if you stand. If the dealer has a 10, J, Q, K or A you lose w/o the dealer even drawing. If the dealer has a 2 down for 11 she'll draw again and nearly half the deck will beat you. The only "safe" card you'll beat is if the dealer has an 8 down for 17. A nine down will push you, and any other down card will give the dealer at least 3 cards she can draw to beat you and one to push you. It's a defensive measure. You're probably not going to win both hands but you have an excellent opportunity to win one and lose one for an overall push or push both hands. And you may even hit 1 or both hands with a 2 for double down possibilities. In this case the risk is worth it.
You split 9,9 against an 8 because now you are the favorite, not the underdog. You have an excellent chance of winning both hands, whereas if you stand you're more likely to be pushed if the dealer has a 10 down. Better to win 2 hands than push with one. You aren't likely to bust on both hands, so in the worst case scenario you should still be able to win one and lose one for an overall push. Of course nothing is certain, it's possible to bust both hands or even for the dealer make 21, but the odds are in your favor.
Standing on 9,9 against a 7 is a bit more tricky and harder to understand. Part of the reason you stand is because your 18 will beat the dealers expected 17 hand. While it may be tempting to split this hand and hit both of your 9's with 10's for a pair of 19 hands, you don't want to take 10's away from the dealer in this situation. You may end up busting one hand and take what would appear to be an almost certain winning hand into an overall push if you split. Worse yet, if the dealer doesn't have a 10 down, and you take 10's the dealer would have drawn you may well be taking cards away from the dealer that would have busted her. A seven card up gives the dealer a lot of outs. And if you split your 9's and don't hit them with 10's you may well bust. So it's better to stand on 9,9 against a 7 even though it may not seem too logical on the surface.