The opener is the newest baseball strategy. Although there are some opener "spin-offs", nothing is quite like the opener.
Basically, the opener is where you put a relief pitcher in the game to start for 1 or 2 innings, and then the starter comes in for the rest of the game.
The thought process behind the opener is that a better pitcher can face better hitters so your starting pitcher doesn't have to. And while effective, teams haven't really adopted this strategy. As much as I would love to see an Oliver Perez start a game, I don't think that all teams will adopt the opener.
Alright, I know what you're thinking. You're thinking about why all teams just won't go ahead and adopt the opener. There are 2 reasons that I can think of, but there are undoubtedly more. The first is that teams are just resistant to change. Wonder why Moneyball was so revolutionary? The second is that it tires a team's bullpen. Starting pitchers can get yanked after 5 innings, but if they're pulled after the 6th inning, a team has to put in their higher leverage guys. If a starter was just starting a game like normal and they were yanked after 5 innings, teams get to put in people who can go 2 or 3 innings. Going into the 7th, teams are less likely to do that, instead opting to put in higher leverage guys. And teams don't like the idea of their higher caliber players being called on 100 times a year (it makes them more likely to get an injury).
But, the opener is still effective and just downright works. That's what teams like. Do you know what's really not popular for the opener? The 2018 AL Wild Card game.
For the Wild Card game in 2018, the A's (small budget team) were facing the Yankees (most feared team in baseball), so naturally they wanted to try a strategy to increase their chance of winning the game.
So they chose the opener, and how did it work? Terribly. The A's decided to start RHP Liam Hendriks which at the time seemed, questionable? When you look at Liam Hendriks' 2018 stats, you see what the critics see. The 4.13 ERA with a 4.33 FIP. But, when you look deeper you discover...
Okay, you still discover a 4.13 ERA with a 4.33 FIP.
So Hendriks got blown up, and that is the most well known occasion of the opener.
But then there was also Brewers manager Craig Counsell, who decided that he wanted to be a sneaky-sneak and try a tactic similar to the opener. So naturally, he decided to fake a starting pitcher. I know, it sounds very weird, but I promise it's possible. Remember, he tried this in the NLCS.
So Counsell went ahead and announced that Wade Miley would be starting the game. Miley faced one batter, walked him, and then got pulled in favor of Brandon Woodruff. Why did he do this? Because L/R matchups matter. Miley is a RHP, and Woodruff is a LHP. Sadly, it failed miserably as the Brewers ended up losing the game, and eventually the series.
So, the opener is a baseball strategy that is amazing. That's all you need to know.