If you speak of football as in the UK soccer and rugby the studs are there to give the player grip on grass and mud covered surfaces. In rugby they are important from the perspective of grip to push...
For grip. When boots were first worn they were working boots and the studs were flat. Protruding studs made of wood were created and these were nailed into the shoe sole. These later were made of...
It is technically still allowed, but it is rarely phrased like that. The key is, does the referee feel there was the intention to move towards the ball, or was there an attempt to move the hand/ arm...