Abso-bluddy-lootely!
Injured - can't play? Get orrff the court!
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If you are fit to play - you are fit to play any shot delivered. If you are not capable of returning any particular shot - tough. Regardless of it's injury or training or basic ability.
This kind of 'be kind to the poor injured player' could be seen as a result of the namby pamby - 'no-one loses' attitude that has infected schools from infants to seniors. The problem with 'no-one loses' is 'no-one wins' either.
Life may not be a full-on, blood at dawn competetion throughout - like it was in the days of cave men - but significant elements of it are. From getting a job to almost all sports, and certainly all competative sports (the clue's in the name). Children who are never allowed to feel the sting of losing to a better competitor (or sneakier cheat) never learn to sharpen up their game to do better next time. Why improve if you always get a lolly regardless of how bad you are? Why make any effort if you only get a lolly the same as the useless lump who fell over at the first hurdle?
You don't have to be soft on you opponent to be 'sporting'. Hell, I'm no sportswoman, but I will hit any weakness in an intellectual sparring match.