20 Reasons Why Your Team is Underperforming

Assuming you are fortunate enough (thank your lucky stars!) to have a group of self motivated, highly competent, and all-round team players as your team members, but lately you've noticed a sudden drop in their performance. What's the problem?
Upon close examination, the problem can be found in one or more of these four areas:
Leadership
People
Scope
Schedule
Leadership - Insufficient or inopportune support, sponsorship and direction
Ambiguous (or confused) goals and objectives
Too many goals - setting unrealistic expectations
Too many unproductive distractions like meetings
Too hands on - Micromanagement
Too hands off - Macromanagement
No or too little feedback
People - Deficits in unity and teamwork
(Individual)
7. Lack of required skills
8. Not enough challenge
9. No enough incentive
10.Personal troubles
11. Work burnout
12. Feeling unappreciated
13. Lack of appropriate tools, equipment, supplies, etc.
(The Team)
14. Not enough capable bodies
15. Clash of personalities
16. Uneven workload or job assignments
Scope - Does everybody understand what we are trying to achieve?
17. Vague or obscure requirements
18. Bad planning or no planning
Schedule or Time - Lack of any sense of urgency - Deadline? What is that?
19. No specific deadlines given - A very common scene in R&D
20. Deadlines are not enforced
Lastly, here is a real world interpretation of the famous project management triple constraints (Scope, Time and Cost):

"Productivity never is an accident. It's always the result of a dedication to focused effort, intelligent planning, and excellence." ~ Paul Meyer
Related posts: What is the BEST team structure?, 12 tips on building a high performance team