What's with the black lines?

It's called "eye black" and they put it there to prevent glare and reflection off the top of whatever bone that is (cheek bone?) Just below your eye

Some tend to use it a little more for decorative purpose, thus the extra lines, shapes, etc

What joc said. I seldom see other athletes doing it though, so I often wonder how necessary and effective it actually is.

it's just the 'look'. however it does look kinda sexy on a female football player.

Other athletes, most notably lacrosse layers do it. The black grease will reduce glare and improve contrast. The improvement is minimal but why not spend a few pennies on some grease when you have less than a second to get your hands in exactly the right spot.

Bryce Harper - baseball

Yeah - I think lots of baseball players also use-it supposedly to help w/ the sun's glare but they seem to also use it at night I assume to help w/ the glare from the strong lights

Bryce Harper is the guy who used to look like Alice Cooper with all the eye black, right? That was on his rookie uear..
Os he still dlong that?

Not to the same extent, but he wears it on occasion.

Baseball players were the first to use it. I never used it when I played but some guys liked it. Other guys were superstitious about using it. Felt they played better when they wore it.

Lights and/or sun glare. Ice hockey and baseball (esp. outfield) players deal with similar issues and are sometimes seen with it. Soccer goalies rarely. Rugby often. It works; used to use it when I played ball in undergrad. Don't know why we don't ever see it on basketball players.

"... Don't know why we don't ever see it on basketball players ..."

Was thinking the same thing - most leagues have pretty-strict rules w.r.t. what the players can wear - perhaps for some reason the NBA banned this?