Can a pitbull kill a rottweiler?

Depends on the pit bull; depends on the Rottweiler. It is important to consider that dog fighting is illegal in the US, so such contests, while they may happen, are not likely to.

Speaking objectively, such a contest is going to depend most on the abilities and tendencies of the animals in question:

Pit Bulls:

• Strong
• Fast
• Light (weigh 22-110 lbs.)
• Prone to aggression if trained to be
• Loyal
• Protective
• Eager to please
• Bright, but not markedly intelligent as a breed
• High pain tolerance

Rottweilers:

• Powerful
• Fast
• Heavy (95-180 lbs.)
• Calm
• Loyal
• Very protective of family
• Eager to please
• Very trainable (highly intelligent as a breed)
• High pain tolerance (especially in protect/attack mode)

Pound for pound, the Rottweiler will generally dominate the average pit bull, but every dog has his day.