With Great Speed...
...Comes great responsibility. Many people seem willing to overlook Nyjer Morgan's numerous offensive problems because of his excellent speed, which is also the key to his defensive prowess.
Last year, this argument didn't seem crazy. Morgan's UZR/150 of 34.7 was excellent and his stolen base success rate of 71% was respectable.
This year the story is much different. Though one incident a season does not make, the consensus seems to be that Morgan has not played the outfield up to par this season. And he's not running all that great either. His bunt-happy ways are also not working out so well this season (18.2% of Morgan's bunts are going for hits this year versus 30.8% for his career).
But offense was never really Morgan's game; his disappointing career .322 wOBA is pretty much all that matters from an offensive standpoint (wOBA incorporates and assigns appropriate weights to nearly all offensive contributions a player makes. It is a rate statistic like OBP). It has been shown that stolen bases rarely add much to a team's offense, and even the most prolific base stealing seasons of all time, Rickey Henderson's 1982 season for instance, contributed little to their team's overall record (See "What if Rickey Henderson had Pete Incaviglia's legs?" in "Baseball Between the Numbers.").
That is why Morgan's defensive shortcomings this season have been so painful. Last year, Morgan, mostly on the strength of his fielding, was tied for third best center fielder in the Majors. This year, he is tied for 2nd worst. (I determined these rankings by looking at WAR, a metric that incorporates nearly every contribution a player makes on the field. You can see WAR ratings at fangraphs.com under the "value" tab of a player's, team's, or league's page.)
Morgan's poor defense this year, then, has done much more than just produce a humorous Youtube video. It has been incredibly costly to his value and to his team's success.
Nyjer Morgan just celebrated his 30th birthday. Because of his age, his speed will most likely dissipate soon, and so will his skills, most of which stem from that speed. In light of this, Morgan needs to seriously think about his defensive problems. His speed is not gone (He has a 6.9 speed rating this year versus 7.1 career), so he must be getting the fundamentals wrong. If he can't find any other reason, he at least owes it to his team to play better. It's certainly within his capabilities.