This Arizona Cardinals fan is showing a classic fear expression in her mouth and neck in the fourth quarter of the game against the 49ers. Notice how this lady's mouth is stretched wide and downward - often with this classic arch. The muscles beneath the lower lip become bunched-up - giving the appearance of a protruding chin. Her neck muscles (platysma) are also tightly contracted. This is not a full-on fear expression however, since her eyes show little involvement. With more pronounced fear, her eyes would be opened very wide - what I call "White and Wide". Notice also that her hands are in a praying position - this is a very common emblem seen at sporting events - almost always at the end of the game/match.
We tend to think of fear arising from a life threatening event or an extreme situation - which is of course very true - but it is also very common that fear is expressed over a more everyday event - like a football game or a business-related issue as long as there is significant emotional attachment. As with any emotion, the expression of fear may be prolonged or very fleeting. Fear is an extremely common microexpression - appearing for less than 0.5 of a second and as little as 0.04 of a second!