Where the defendant is carrying out an activity that demands a certain level of skill, he is expected to meet the standard of the reasonable person practising that activity. If he is a professional, he will be expected to match the standards of the reasonable professional; if he is an amateur, he will be judged against the (possibly lower) standards of the reasonable amateur so long as the activity is one that it is reasonable for an amateur to attempt.
Philips v Whiteley  1 All ER 566, Goddard J
A woman developed an infection after having her ears pierced by a jeweller, and the judge said the relevant standard was that of a reasonable jeweller rather than that of a surgeon. D had sterilised the needle in a flame before leaving his shop, and dipped his fingers in disinfectant when starting the procedure, and that was enough.
Wells v Cooper  2 All ER 527, CA
A man fitted a door handle in his own home; a visitor pulled on the handle and it came away in his hand, causing the visitor to fall down several steps. The Court of Appeal said D was to be judged against the standards of a reasonably competent carpenter, but not necessarily against the standards that would be expected of a professional carpenter working for reward. Even in these early days of DIY, this was the sort of job that a reasonable householder might do for himself, and that was the appropriate standard.
Condon v Basi  2 All ER 453, CA
A reckless tackle in a Sunday league football match led to a broken leg. The Court of Appeal said that participants in competitive sport owe a duty to one another to take all reasonable care having regard to the particular circumstances. The standard of care required is objective and is not adjusted to the skill (or lack of skill) of a particular player, but it does vary with the circumstances and a higher degree of care is required of a player in a First Division match than of one in a local Sunday league.
Luxmoore-May v Messenger May Baverstock  1 All ER 1067, CA
A provincial firm of auctioneers and valuers assessed two paintings as worth about £50 each. The paintings were sold at auction and fetched £840, but five months later they were resold for £88,000. The former owners of the paintings sued for the difference, but the Court of Appeal said the standard of care demanded of DD was that of a general practitioner rather than that of a specialist. By that standard they had carried out their work reasonably competently, and an error of judgement (such as failing to recognise a painting by Stubbs) did not necessarily breach the duty of care.
Smoldon v Whitworth (1996) Times 18/12/96, CA
A young rugby player suffered a broken neck when a scrum collapsed, and sued the referee for not taking steps earlier in the match to prevent such dangerous play. The standard of care required of a referee depends on all the circumstances, said Lord Bingham CJ, and the referee could not hope to see everything that went on; but in the instant case even D2's own expert witness had conceded that D2 had not come up to the standard to be expected of a reasonable referee. A decision in P's favour would not open the door to a plethora of claims by players against referees, provided all concerned appreciated how difficult it would be to establish that a referee failed to exercise such care and skill as was reasonably to be expected in the circumstances of a hotly-contested game of rugby.