I've bet 3ways on soccer and NHL from time to time.
In soccer, if i bet the underdog at +1, and at end of regulation time it was tied 1-1, then i'd lose and the "tie" wager option would win, hence the 3way option.
And if the underdog at +1 was winning at end of regulation, say, 2-1, then the bet would be a winner.
But, if the underdog at +1 was losing by 1 goal, say, 1-2 at end of regulation, most books call it a push. Because you bet +1 and it ended after regulation being a one goal difference.
Same w/ NHL.
After 3 periods, there can either be a team losing, a tie, or a team winning.
If i took an underdog at +1 goal and at end of 3 periods it was tied at 1-1, then the "tie" bet would win, and a +1 bet would lose, or a -1 bet too.
If i took the underdog at +1 and they were winning at end of regulation, then it's be a winner. And if they were only down one goal, say, 1-2, then it'd be a push because they were +1, and they lost by one goal.
MLB should be same concept. At end of 9 innings either underdog is winning, or it's tied and going to go extra innings, or the fav is winning.
So the 3way options are +1, tie, -1
If the underdog at +1 is down one run at end of 9 innings, it should be a push. If not, what's the point of offering the PLUS 1? If the only way the underdog +1 wager can win is IF the underdog is winning at end of 9 innings, then the 3way offer of +1 is irrelevant, right? Like, why offer it, if the underdog has to be winning at end of 9 innings in order to win the 3way?
Go to Bet365 and dig through looking for the rules. Under MLB they don't have anything about 3way wagering, yet they offer it.
If you inquire about it they seem confused in CS and will put you on hold for a long time, then come back with a copy & paste about about how everything is for full 9 innings and extra innings not included.
Even asking CS they suggest you look over the "results" for the game and it will list the winning wagers for everything available. Well, if i go to the game(any MLB game) and scroll through all 100+ wager outcomes , there is not one mention of 3way results. Every other result is listed, but not 3way. Yet, i can wager the 3way at +1, Tie, -1 for 9 innings.