Longtime Orioles star Manny Machado has been traded to the Dodgers, with whom he will step in for the injured Corey Seager at shortstop, likely pushing Chris Taylor to the outfield or second base. With a .315/.387/.575 line, Machado has been baseball's eighth-best hitter on a park-adjusted rate basis, just ahead of Aaron Judge and Freddie Freeman, and he's doing it while playing shortstop.
Machado is almost certainly the most valuable player being traded before this year's non-waiver Trade Deadline, barring an unexpected Jacob deGrom trade. He'll almost surely end up being the most valuable player traded in any of the past few Deadlines, really. (Justin Verlander was a post-Deadline trade last August.) That leads to the inevitable question: Have there actually been Deadline trades like this? When do we see stars at this level being moved?
The only good way to do this is to use Wins Above Replacement, an imperfect-but-good-enough metric that accounts for hitting, baserunning and fielding, and allows for comparisons across eras. For example, a 2-WAR player is always "league average." A 4-WAR player is All-Star level and 6-WAR players are superstars. Last year, per FanGraphs, Judge led the bigs with 8.2 WAR. Machado accrued 3.6 WAR in this season's first half, putting him in the Top 15. He's projected to end the year with 6.2 WAR, which would equal his total from his very good 2015 season.
(It's worth noting that Machado has managed to compile such value while playing a shortstop that hasn't been reviewed very well; by some metrics, he's been baseball's least effective defender at the position. Judge, who has nearly the same hitting line while playing a good defensive right field, has accumulated 4.7 WAR.)
Going back to 1986, which is when the Trade Deadline moved back from June 15 to July 31, how many times have we seen players this valuable traded in July? The answer: not often, especially among hitters.

This list includes some of the most impactful Deadline deals of the past three decades, and since there's not really a meaningful difference in tenths of a point of WAR, you could essentially look at this as four 7-WAR players at the top, and Machado in the group immediately following. Since the top three are pitchers, there's an argument to be made that Machado is the third-most-valuable hitter traded at the Deadline in the 30-plus years since it was moved.
Not all of these deals were created equally, of course, in part because we're showing full-season WAR, not WAR at the time of the trade. Let's group a few of the similar top ones together and see how many echo the Machado deal.
7.6 WAR -- Randy Johnson, 1998
7.3 WAR -- CC Sabathia, 2008
When you think about impactful Deadline trades for pitchers, you think about these two trades, made a decade apart. Johnson made 11 starts for Houston after being traded, and the Astros won 10 of them, as he whiffed 116 hitters and allowed only 12 runs. He was equally outstanding in two National League Division Series starts, though the Astros lost that set to the Padres; it's arguably the most dominant stretch of post-trade pitching we've ever seen.
Sabathia's story is similar. He was having a good-not-great season for Cleveland, then went to Milwaukee and found an entirely new level, completing seven of his 17 starts, throwing three shutouts and posting a 1.65 ERA, though he was hit hard in his lone postseason start. Both Johnson (to Arizona) and Sabathia (to the Yankees) left their new clubs the following offseason.
7.0 WAR -- Cliff Lee, 2010
6.3 WAR -- Cliff Lee, 2009
Let's lump these together, since Lee was traded three times in less than a year, twice in July, at the peak of his considerable powers. In 2009, he went from Cleveland to Philadelphia, which is how Carlos Carrasco ended up in Ohio, and he was pretty good on both sides, posting a 3.14 ERA with Cleveland and 3.39 ERA with Philly. But he was fantastic in October, putting up a 1.56 ERA in five starts as the Phillies reached the World Series.
Lee was dealt to Seattle that offseason for no one the Mariners would ever regret losing, then after a strong 13-start stretch with Seattle (2.34 ERA), he was sent to Texas for a package headlined by Justin Smoak. Lee wasn't quite as great for the Rangers (3.98 ERA), but he again excelled in the playoffs (2.78 ERA) as his team reached the World Series. Lee would re-sign with the Phillies that offseason.
6.5 WAR -- David Price, 2015
6.0 WAR -- David Price, 2014
Speaking of ace lefties traded two years in a row: Price went from Tampa Bay to Detroit in 2014, then from the Tigers to the Blue Jays in '15. Price was only OK as a Tiger in '14 (3.59 ERA, one good start in a losing American League Division Series), but he was exceptional as a Blue Jay down the stretch in '15, striking out 87 with a 2.30 ERA in 11 starts. He struggled in four starts that October, then departed for Boston.

6.9 WAR -- Mark Teixeira, 2008
6.5 WAR -- Scott Rolen, 2002
Both of these star corner infielders turned it on after their trades, though there's going to be one significant difference here. Teixeira was traded two Deadlines in a row, so he'd only been with the Braves for about a year before he was sent to the Angels, where he hit a sensational .358/.449/.632 before hitting .467/.550/.467 in the ALDS; he'd sign with the Yankees after the year.
Rolen also had a fantastic post-trade run, hitting .278/.354/.561 and drilling a homer in the NLDS. The caveat here is that there was a lot more going on than a regular "rental trade," because he was eager to leave Philadelphia and had requested a trade.
6.1 WAR -- Randy Velarde, 1999
We honestly don't have a great explanation for this. The longtime utility player had a career .268/.344/.400 line headed into his age-36 season, when he put together a .317/.390/.455 line in 711 plate appearances. Velarde was traded from the fourth-place Angels to the second-place A's in July. It mostly didn't matter -- though he was even better for Oakland than he had been for Anaheim.
5.9 WAR -- Manny Ramirez, 2008
5.8 WAR -- Yoenis Cespedes, 2015
Finally, this pair of corner outfielders had enormous impacts on their new teams. Ramirez had long been a star with Cleveland and Boston, but he turned it on to an entirely new level with the Dodgers, hitting .396/.489/.743 down the stretch and a ludicrous .520/.667/1.080 in the postseason before entering free agency. (He'd later return to the Dodgers, but not until the following March.)

Cespedes cost the Mets Michael Fulmer and Luis Cessa, but they surely don't regret it. He had hit 18 homers for Detroit in 102 games, then hit 17 for New York in just 57 games, helping to push the Mets into the postseason. (He cooled off in the playoffs, hitting just .222/.232/.352.) Like Ramirez, he was a free agent for several months before returning.
So what does this all mean for Machado and the Dodgers? The good news is that none of these high-level players went to a new team and failed to perform. Most of them did better, some wildly so, though there's got to be at least some concern over Machado's huge home/road splits. The point here is that you just don't see players of this caliber dealt in July very often; it happens, on average, about once every three years. When it does happen, the performance is almost always there. That is, of course, what the Dodgers are betting on.