Possible Clues:

• Cause of infuriation on trail
• Source of extreme provocation
• Provocative article in communist paper
• Provocation to bull
• Colourful scrap for bait for bully beef
• Cause of infuriation
• A neat way to infuriate?
• Reputed to annoy bull
• Radical journal with capacity to incite
• Proverbial bull enrager