I think the flat hard surface is to ensure that the patients arm will not move when the needle is administered since it is usually critical that the needle is inserted in the correct vein which is only a fine target requiring careful positioning of the needle.
What article? please start posting the desired article with your question.
double blind procedures improve identification because it removes bias from the equation.
Well because this is health I am assuming they are referring to the health side of the sport. The concussion rate in the sport is super high, higher than most sports even with the padding and helmet protection. It is also a high contact sport so injuries are bound to happen.
