The police officers guarding the G8 summit in Gleneagles have been trained to expect anything from aggressive demonstrators to devious terrorists.
What they probably have not been briefed on, though, is how to react when the most powerful man on earth comes hurtling towards you on a push bike.
Such was the fate of one Scottish police officer who suffered a bruised ankle yesterday evening after being involved in a collision that also left George Bush nursing a few grazes.
It seems the US president had decided to celebrate his 59th birthday with a two-wheeled spin around the grounds of the Gleneagles hotel when a light drizzle - and a minor disaster - struck.
A White House spokesman said Mr Bush had been pedalling along for about an hour at what he termed a "pretty good speed" when he hit the officer, who was on foot.
Scott McClellan said the president had scraped his hands and arms and they were bandaged by Richard Tubb, the president's doctor.
"He was wearing a helmet," Mr McClellan said. "The accident occurred on asphalt. His scrapes were mild to moderate.
"The president was mostly concerned at the officer's condition and spent time talking to him and asked his physician to monitor him in hospital," Mr McClellan said.
Mr Bush's mountain bike was damaged, forcing him to return to the hotel in a van.
The police officer, from the Strathclyde force, was taken to Perth royal infirmary and treated for a slight ankle injury. The officer was released last night and returned to his duties.
Mr McClellan said the president, who was sufficiently recovered to dine with the Queen and the Duke of Edinburgh last night, had spoken to the officer and was intending to phone him later to check on his progress.
Mr Bush became a devotee of cycling a couple of years ago after a knee injury forced him to give up running. But his leisure pursuits are not without their periIs. In May last year he fell off his mountain bike, grazing his chin, top lip, nose, knees and his right hand while riding on his ranch. He also came to grief on a motorised scooter in June 2003. On that occasion, however, neither vehicle nor rider was damaged.
In January 2002, he survived a potentially fatal encounter with a pretzel.
U.S. President George W. Bush crashed his mountain bike into an unfortunate police officer in Scotland. 

Mr. Bush, who celebrated his 59th birthday last night was cycling on a bike around the Gleneagles Hotel, where he is staying for the 31st G8 summit, when he, perhaps partially due to the bad weather, crashed into one of the police officers responsible for his and the other leaders' safety. 

The officer had to be taken to the hospital having suffered a twisted ankle whilst Mr. Bush, who was wearing a helmet, only suffered minor bruises despite landing on asphalt. The president had to return to the hotel by van because the bike was too badly damaged.

Bush has been involved in two similar accidents during his presidency. In 2003, he fell off a Segway personal transporter, and in 2004, he fell off a mountain bike.