Pittsburgh Steelers quarterback, Ben Rothlisberger is shown in this image with a very characteristic "Bitter Smile" (Ekman) combined with a "Inward Lip Roll" (ILR) after his team's loss to Tim Tebow and the Denver Broncos, 29-23 in overtime. This light-lipped, concave-down closed mouth expression is highly consistent with the emotions of regret and bitterness. Incredibly, most everyone believes they are displaying an neutral expression or even a subtle smile - when in fact this is a form of a frown (ergo the oxymoronic label "bitter Smile"). We all make this expression much more often than we believe, and it is one of the best and most ubiquitous examples of how human beings routinely lack objectivity regarding our own appearances - particularly those accompanying negative emotions.
Additionally Rothlisberger is rolling his lips inward so that they are no longer visible. This Inward Lip Roll is a strong signal of anxiety. Additionally, it is very often associated with a considerable effort to control/minimize an outward expression of a negative emotion. It's as if the psyche is calling on inner reserves to control the loss of temper.
This characteristic combination of expressions exampled here by the Pittsburgh QB is seen on the sports field either after an injury or loss - and rarely at other times. Rothlisberger endured both on Sunday.