Do I tap a creature when it fights? Can a creature with summoning sickness fight?

Question

If a card has text: target creature fights (another creature), do I have to tap the target creature? Can I target a creature, that has summoning sickness this way?

Answer 1

No you don't tap the creature; even tapped creatures can fight. If you had an instant fight card you could use it during combat as a combat trick. Summoning sickness only effects combat, and tap abilities; fight cards can certainly target a creature with summoning sickness.

The relevant rules from the comprehensive rule book:

701.10. Fight

701.10a A spell or ability may instruct a creature to fight another creature or it may instruct two creatures to fight each other. Each of those creatures deals damage equal to its power to the other creature.

701.10b If a creature instructed to fight is no longer on the battlefield or is no longer a creature, no damage is dealt. If a creature is an illegal target for a resolving spell or ability that instructs it to fight, no damage is dealt.

701.10c If a creature fights itself, it deals damage equal to its power to itself twice.

701.10d The damage dealt when a creature fights isn’t combat damage.

Also relevant, since it isn't combat damage, first strike doesn't do anything, but abilities like lifelink, or deathtouch do work.

Answer 2

Fighting doesn't require tapping, and it doesn't care if one of the creatures has summoning sickness.

While fighting has some similarities to combat (namely 2 creatures deal damage to each other equal to their power) it is not actually combat, so things that are required for combat (like tapping to attack and not having summoning sickness) are not required for fighting.

701.10a A spell or ability may instruct a creature to fight another creature or it may instruct two creatures to fight each other. Each of those creatures deals damage equal to its power to the other creature.

701.10d The damage dealt when a creature fights isn’t combat damage.