In 2006, the Houston Rockets drafted small forward Rudy Gay and then abruptly traded him to the Memphis Grizzlies for 5-year veteran swingman Shane Battier. Since then, Rudy Gay has gone on to average 18 points and 6 rebounds for the Grizzlies, and they have since rewarded him with a 5 year, $82mil contract which he is now entering the third year of.
The trade of Rudy Gay for Shane Battier is commonly cited as one of Daryl Morey's failures; he traded a young, budding star for a role-playing "asset" that he's so fond of. The problems with this stance are so enormous that one doesn't even know where to start.
First off: Daryl Morey was not GM of the rockets until May of 2007. Carroll Dawson was still the GM of the Rockets during this trade, and Morey was the assistant manager. Even if Morey influenced this trade, CD was the one calling the shots. You can't blame Morey for something that happened before he was in charge.
Secondly, Shane Battier is just a flat out better player than Rudy Gay. Battier not only does he beat Gay in the intangibles (commonly cited as Battier's biggest strength) but in the statistical departments as well. In 2011-12, Rudy Gay's 6th year in the league, he averaged 19 points per game on 52% true shooting. He also picked up 6.4 rebounds per game, .8 blocks per game and 2.3 assists per game, while turning the ball over 2.5 times and stealing the ball 1.5 times. He totaled .120 win shares per 48 minutes (how many wins he produced for his team in 48 minutes). In 2006-07, Shane Battier's 6th year in the league, he averaged 10 points a game on 58% shooting while collecting 4.1 rebounds, 2.1 assists, 0.7 blocks, 0.9 turnovers and 1.0 steals. He totaled .144 win shares per 48 minutes. Statistically, Battier is very similar to Gay. Gay is a slightly better rebounder, but Battier more than makes up for this by having a much better assist to turnover ratio and collecting a much better shooting percentage. Gay is a classic ballhogging chucker: he scores a lot of points by putting up a lot of shots, but not that many of them go in. His incredibly bad assist to turnover ratio shows just how much of a ballhog he is. Battier, on the other hand, is a very good three-point shooter who rarely turns the ball over. He also plays much better defenender than Gay.
Finally, even if Rudy Gay was a better player, Battier fit the team at the time much better. The Rockets were already contenders with Yao Ming and Tracy McGrady as centerpieces, and they did not need another star that would demand the ball as well. McGrady was already playing the role that Gay would play, and Battier could hit 3s and play defense, something that the team needed.
In short, if you think that Morey was wrong in trading Rudy Gay for Shane Battier, you're a moron in multiple ways.
Edit: I made an error in the statistics by forgetting that there were fewer games last season. This has been corrected.