So, I went through a bunch of different editions of Hoyle’s Rules for poker, looking for evidence of string betting rules.
Note that after Hoyle, many other writers and editors have published their own versions under his name. I’ve attached photos of pages from Foster, Coren and Morehead. Many pocket and other editions tend to leave out a lot of details about the finer points of poker, compared to these.
1) Foster published his expansion of Hoyle’s gambling rules starting in the late 19th century into the early 20th. From what I can tell he was considered the authoritative source on poker for a very long time.
His edition of 1916 does not use the term string betting, and does not give a lot of detail on how exactly to place a bet, but he does have this to say... One could infer that a string bet would be disallowed because it would require the bettor to take his hands off the first batch of chips brought forward:
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Foster elsewhere does use the now-despised language of “see your bet” with the option of then “raising.” He seems to care more about the action of putting in chips and releasing them, than about verbal announcements.
Jumping ahead a half-century to 1961, Morehead has a long section on “Method of Betting” which again does not use the phrase “string bet” per se, but does seem to place some of the same limitations on string betting with which we are familiar today.
He also puts a strong emphasis here on *announcing* your bets, with the potential of the bet being limited if no announcement is made:
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Note that Morehead also published an edition of poker rules in 1950, but I do not own a copy, so I can’t say whether this passage was in it or came a decade later.
(FWIW, neither Foster nor Morehead seem to anticipate a problem discussed a while ago on PCF, that of a player using *two hands* to bet separate stacks of chips. In theory the player might not be taking his hands off the first batch before setting the second one down, but I think it’s pretty clear the authors would have considered that irregular.)
Lastly, and at last, Coren’s version of Hoyle from about the same time (1960) explicitly uses the term “string bet,” which he also calls an “installment bet”:
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This appears to be pretty much the current rule.
There are many different versions of Hoyle between 1916-1950/60, of course, but a lot of them seem to just repeat the others or omit mention of betting methods entirely.
Generally, these books plus Roberts suggest to me that prohibitions against string betting have existed in various forms long before the WSOP began. However, those rules seem to have varied in their strictness and particulars. And my guess is that many gambling establishments and private games did not begin consistently enforcing them until the past 25-30 years.