Shifting Trends is an irregularly published series about how baseline poker strategy has changed over the past five or so years. It is written from the perspective of a low-to-mid stakes online Sit-and-Go, Spin-and-Go and multi-table tournament semipro; some of the trends we’ll look at may differ when it comes to live and/or cash game play.

In the last Shifting Trends piece, we took a look at a case where a move which used to be a reliable indicator of strength – the preflop minimum 3-bet – has begun to be used the opposite way by some players. This time around, we’re going to look at a move which has evolved in the opposite way: the suspiciously small river bet by an out of position player.

Like most of the specific moves we’re discussing in this series, a tiny, out-of-position river bet doesn’t accomplish very much from the point of view fundamental strategy, except in the case of going for thin value from an opponent you can range quite narrowly. Much more often, it’s a form of leveling move, relying on assumptions about how it will look to the opponent, and what they’re likely to do in response.

The post-oak bluff

At one time, such a bet could often be what Doyle Brunson called a “post-oak bluff” in his 1979 classic book Super System. When used this way, the tiny river bet operates on the assumption that the opponent will fold his weaker marginal hands regardless of the pot odds being offered to call – or, perhaps, that he will read the sizing as extremely strong, and fold for that reason.

Recreational players’ understanding of fundamental strategy is much, much greater in 2015 than it was in 1979, and even back then, Brunson criticized it as a “gutless,” amateurish move. For this reason, one rarely sees really tiny bet sizes as bluffs these days.

The one exception is in a pot which has been checked on the flop and turn, facing an opponent who is seen as both tight and straightforward. In that sort of situation, one does see players occasionally fire off a min-bet with a hand like 8-High, as it’s worth a shot if it could get the opponent to fold better high-card hands. Even then, once such a bluff has been called and shown down, on subsequent occasions it’s as likely to be a trap, or even a thin value bet with Ace high, as it is to be a bluff again, unless the player in question is very poor indeed.

The blocking bet

I’m not sure that the post-oak bluff was ever widespread, because if it was, it was before my time. When I got into the game, however, in the early boom years, there was a popular strategy going around of using a small sizing when out of position on the river as a so-called “blocking bet.” The recommended time to do this was when you held a marginal hand, and your opponent was likely to as well, and your objective was to get to showdown as cheaply as possible.

The idea behind this move was that your opponent would be likely to bet her marginal hands if checked to, but likely to raise with them for fear of only getting called by monsters. By doing the betting yourself, rather than checking and calling, you could effectively name your price, and be able to find out whether your hand is good for a lesser amount of chips than your opponent would have been likely to bet if given the chance.

This is clearly a highly exploitable move, in that it works really well if your opponent behaves as expected, but if she realizes what you’re attempting to do, she can easily raise her entire range, at which point you’ve accomplished exactly the opposite of what you intended. For that reason, making blocking bets against players who know about blocking bets is not typically going to work out very well, particularly if you do it consistently.

That said, many players, both live and online, still have ideas about “correct” strategy based on highly outdated information, so the blocking bet is still seen a fair bit, particularly from weaker players. There are still even some people still recommending it to others. One strong tell that your opponent may employ river blocking bets is if he’s shown a tendency to bet small on other streets as well.

The inducing bet

The blocking bet has been around a long time now, and almost everyone playing today has done at least a little reading. As such, you’ll rarely find anyone unacquainted with the concept, which means that even those players who still use the blocking bet habitually have found themselves facing raises in response, and may even be raising people who attempt to do it to them. This leads us to the next stage in the evolution of the small river bet, which is as an inducing move.

Obviously, betting small with marginal hands with the intention of folding is a disastrous idea if your opponent is going to raise most or all of his range. If he’s going to that, however, then what you have instead is an amazingly useful tool for getting value. If you bet big with a marginal value hand, our opponent may fold most of the things you beat, but checking can also be seen as a trap, particularly if you’ve been aggressive on previous streets. So, if you bet small, your opponent may read that as weaker than checking and raise in response, thus accomplishing the goal of getting him to put money in with the weaker parts of his range to compensate for those times that you’re beat.

A good range for an inducing bet may not be much different from that for a blocking bet, then. Perhaps a little stronger, but not necessarily much so, since it is essentially a variation on the usual check-call bluff-catching line. The difference is in the intended follow-up: folding to a raise if the player is trying to block, calling the raise if the intent was to induce. Monsters can also be included in an inducing range, but don’t have to be; some players will instead make a normal-sized or oversized bet with the top of their range, or attempt to check-raise.

Staying ahead of the curve

As exploitable as it usually is, the small river bet is a tricky one to take advantage of because it has three possible meanings. Just as its effective use depends on eliciting a predictable response, the counter-strategy revolves around guessing what the predicted response is and doing the opposite. If you think that the opponent believes he can bluff you off Queen High with such a bet, then you should be calling with hands all the way down to Queen High and perhaps raising as a counter-bluff with worse. If you think he’s blocking, then you should always raise. If you think he’s inducing, then you should actually fold the very bottom of your range, call with most marginal hands, and only raise your monsters. But what if you’re not sure?

Fortunately, there’s an easy way to at least not be exploited by these tiny bets, which is to treat them as equivalent to a check. That is, if you were planning on checking back, then you just call (unless there aren’t even any bluffs you can beat), as paying off such a small bet is never a huge mistake if you have any chance at the pot. If you were planning on betting, then you raise to exactly the amount you would have bet anyway. Under this strategy, the opponent’s tiny bet will only be better than checking in a very limited number of cases (where you pay off with very weak hands that you would neither bluff with, nor call a larger bet), and the benefit in those cases is likely outweighed by the value he loses on occasions when you would have called a slightly larger bet. An extremely astute opponent might adjust by going for extremely thin value with his weakest showdown hands like Ace High, but you’ll quickly pick up on that and can counter-adjust at that point.

If you want to get into exploitative play, however, then there are three things to look at: the opponent’s overall style, the way the hand has played out, and whether either of you have made such a bet before and had it shown down.

Post-oak bluffs will usually come from either very bad players, or much more rarely, from a good player who thinks he’s got your game thoroughly figured out. They’re also only likely to happen in cases where both you and your opponent have many very weak hands in your ranges. It’s a move that most often comes up – especially from the bad players – when several streets have been checked, and it seems hard for anyone to have much. From a good player, it could come on a very draw-heavy board where everything missed, but only if he has cause to believe that you’ll surrender your missed draws to any bet rather than fighting back.

Blocking bets and inducing bets, on the other hand, are much harder to distinguish based on the run-out of the hand, because they’re made with similar ranges and the whole point of an inducing bet is that it’s meant to be read as a blocking bet. The biggest clue that you’re looking at a blocking bet is that your opponent is a slightly-losing player with an ABC style of play – that is, someone who probably learned to be a winning player in the pre-Black Friday years, but then failed to adapt. Conversely, someone putting up good numbers in recent years is much more likely to be inducing, at least the first time you see such a bet.

Once one or more hands have been shown down following this kind of small bet, however – whether by you or by them – then the opponent’s identity matters much less than where you think you are in the leveling war. Even the players who are fond of blocking bets have by now figured out that people will try to exploit them; even if they still believe they’re “blocking,” when faced with a raise they may question whether you’re on to them and decide to look you up, changing their blocking bet into an inducing bet retroactively. Once this dynamic begins, you have to expect that the opponent is employing a mixed strategy with the small bets and make your decision accordingly: you can either try to anticipate their change-ups and win the leveling war, or you can go back to the treat-the-small-bet-as-a-check line and mostly avoid the issue that way.

Alex Weldon (@benefactumgames) is a freelance writer, game designer and semipro poker player from Montreal, Quebec, Canada.