It only takes a split second whether someone comes out as a victor or a loser in combat. The person can try to remember it later on to see what errors were made in order to become a better fighter in the future.
Such things also happen in competition which is why it is best for the student to be familiar with the various aikido moves at all times.
For instance, in Ai hanmi Iriminage a person grabs the attacker by the neck and forces the opponent to the ground.
In Ai hanmi Kokyuho, this is similar to the first with the difference of extending the arm a little farther in order to achieve maximum effect.
Should the attacker have a knife, a good aikido move to use is called Katate Ryotemochi in which the individual uses both hands to block the weapon used by the attacker and disarming it before putting the person on the ground.
If the individual is able to get behind the attacker, perhaps doing Ushiro Ryokatatori will be a good idea. This will allow the student to grab both shoulders of the person. Should the individual be tough, perhaps applying Ushiro Kubishime, which will temporarily cut the air supply until the assailant is unconscious, is...