Football players use the black marks under their eyes to absorb light and reduce glare which improves their vision on the field.
Eye black is a grease applied under the eyes to reduce glare. It is often used by football, baseball, and lacrosse players, where sunlight or stadium lights can impair vision of an airborne ball. It is a form of functional makeup or war paint. Traditional grease consists of beeswax, paraffin, and carbon. Anti-glare face strips that emulate the grease are also commonly used. One of the earliest known instances of a player wearing eye black is baseball legend Babe Ruth, who, in or around the 1930s, used the grease in an attempt to reduce sun glare. According to Paul Lukas of ESPN.com, eye black caught on with American football player Andy Farkas. He also states that the original eye black was made from burned cork ashes.
A 2003 study by Brian DeBroff and Patricia Pahk tested whether black eye grease actually had anti-glare properties. The subjects of the study were divided into three groups: wearers of eye black, wearers of anti-glare stickers, and wearers of petroleum jelly. The subjects' vision was tested using an eye chart while being exposed to natural sunlight. The study concluded that eye black reduced glare of the sun and improved contrast sensitivity, whereas commercial anti-glare stickers and petroleum jelly (the control substance) were found to be ineffective. However, the study was flawed because the subjects were aware of which substance was applied, introducing demand bias, i.e., the test subjects could have unconsciously changed their responses during testing based on the fact that they knew which substance they were wearing. Also, the petroleum jelly could have introduced glare that would not occur on natural skin and the study did not test a control condition of natural skin. Sports