1-2 NL. Player A bets $50. Player B goes all in for $76. Player C doesn't announce raise and bets $100. Is player C's bet just a call or a raise? If a raise, what is his min raise amount and why?
It really depends on the card room and the rules they play, there is no definitive "Everyone must play like this" rule. You can find some "official" rules out there but these are generally rules enforced by different poker institutions and are not universal.
Some rooms enforce that you must declare your intent before throwing chips into the pot with penalties. Such penalties may be turning the chips to dead money and folding your hand or forcing you to call in this situation. Here in general Player C would have been forced to call and received change out of the pot from the dealer.
Other rooms will force player C to raise here even if he was just going to call because he has put more in the pot than the previous bet or raise.
In general the most common rule is that you must declare your intent. Here is an example of the TDA rule set for calling:
39: Methods of Calling
Standard and acceptable forms of calling include: A) verbally declaring “call”; B) pushing out chips equal to a call; C) silently pushing out an overchip; or D) silently pushing out multiple chips equal to a call under the multiple-chip betting rule (Rule 43). Silently betting chip(s) relatively tiny to the bet (ex: NLHE, blinds 2k-4k. A bets 50k, B then silently puts out a single 1k chip) is non-standard, strongly discouraged, subject to penalty, and will be interpreted at TDs discretion, including being ruled a full call.
42: Oversized Chip Betting
Anytime when facing a bet or blind, placing a single oversized chip in the pot is a call if a raise isn’t first verbally declared. To raise with an oversized chip, raise must be declared before the chip hits the table surface. If raise is declared (but no amount), the raise is the maximum allowable for that chip. When not facing a bet, placing an oversized chip in the pot without declaration is a bet of the maximum for the chip.
Now again depending on the card room your playing at some force your raise to be double the last raise, so in this case Player C would have to raise a minimum of $152. Others do not and as long as your raise exceeds the previous bet by at least 1 blind the bet is valid. Others rooms will force Player C to exceed the current pot size or at least a percentage of the current pot. So in this case he would have to raise $126 or more.
If you are ever in doubt, always speak to the dealer or the floor-man about the house rules before taking an action your unsure of.
I assume your example is a live Game. In that case, where I come from, player C merely calls when he silently tosses in any amount in a single motion/single bet without specifically voicing his it intention to raise.
I know that depending on your locale, the ruling may be vastly different, however next you find yourself in CT, keep tbe above in mind.