Phillip is an elderly man who lives alone in Mayfield, NSW.One morning Derek, a tourist from Ireland, sees Phillip gardening in his front yard.Derek states:

"Sorry to interrupt you.I used to run a roofing business in Ireland, and I've just migrated to Australia.I've got a building licence.I noticed your roof has some problems with the tiles, and if you don't get it fixed it will leak.Do you mind if I have a look and give you a quote?"

Phillip agrees and Derek uses a ladder in Phillip's garage to climb onto the roof.After climbing back down, Derek tells Phillip:

"It's just as I thought the roof's in pretty bad shape at the front of the house.I strongly recommend you get it fixed.I can do it cheaply if you pay cash up front.The normal cost would be $10,000, but I'll take $2,000 up front in cash and $2,000 in cash when I finish the job.If you agree, I can start tomorrow and have it finished in a few days".

Philip agrees. Derek gives him his mobile telephone number.Phillip withdraws $2,000 cash from the bank.The next day Derek arrives.Phillip pays him $2,000.Derek works on the roof for about 4 hours and leaves.He does not return.

Phillip telephones Derek repeatedly over the next 2 weeks to come back and complete the work.Derek gives Philip a number of excuses as to why he cannot return, including that his girlfriend is in a coma in John Hunter Hospital in Newcastle after being run over by a tram in Hunter Street.

Phillip then tells his grandson Sam what has happened.Sam is a 25-year-old truck driver who is a black belt in Jujitsu and formerly played first grade rugby league for the Macquarie Scorpions.Sam attends Phillip's house and checks the roof.It appears that minor work has been done to the roof.

Sam obtains Derek's mobile phone number from Phillip and calls the number.Derek answers. During the conversation, Sam angrily states:

"I don't know who the hell you think you are, but you can't con my grandfather and get away with it.Unless you come to the house tomorrow and give him his money back, I will hunt you down and break your ducking neck!Be here tomorrow if you know what is good for you!"

Derek does not come to the house the next day and changes his mobile phone number.A few days later, while having coffee at Suspension Expresso caf in the suburb of Islington, Philip and Sam see Derek walking past.Phillip tells Sam: "That's the Irish bloke who took my money".Sam runs out of the coffee shop and shouts: "Hey shonk, stop right there!".Derek runs to a local park, and Sam chases him.When in the park, Derek trips over and falls to the ground.

Sam kicks Derek three times in the ribs, and exclaims: "Think you can cheat an old man?See how you like it?Give me your wallet and mobile phone to pay back what you owe!"

Derek hands over his wallet and mobile phone.Sam opens the wallet, looks inside, and takes all the cash in the wallet.The amount of cash is $500.Sam keeps the mobile phone, and a few days later sells it to a pawn shop for $200.Sam returns S700 to his grandfather and adds $1,300 of his own money so his grandfather has not suffered a loss.

After being kicked in the ribs, Derek walks home in severe pain.At home he calls an ambulance and is take to John Hunter Hospital.X-Rays show Derek has 4 broken ribs.Derek is hospitalised in a ward near his girlfriend who remains in a coma.

Discuss the criminal liability, if any, of Derek and Sam.