The femoral artery is the main one that runs down into the leg. It carries all of the oxygen rich blood needed to keep this major part of the body going. If the femoral artery is cut or broken, as is said to have happened in the Sean Taylor shooting, then this is extremely serious. 10- 15 minutes without medical treatment (or without a tourniquet being applied) would normally mean death.

Fortunately, if prompt medical treatment is given, including blood transfusions and a stemming of the bleeding, then the prognosis is generally good. It depends really on how much blood is lost before the flow is staunched.

Sean Taylor (NOON UPDATE)

Sean is in critical condition in Florida after being shot in the
leg. The injuries are very serious, and according to one team official
"It’s not good. We’re waiting on more details from the hospital." There
is some concern an artery may have been struck, though I have not been
able to get the firmly confirmed.

UPDATE:
Just spoke with a friend of the family who said that Sean lost a
substantial amount of blood and the bullet traveled near the femoral
artery, which is located in the upper thigh. Sean’s father, Pedro, the
chief of police in Florida City, Florida, is with him at the hospital,
according to the source. They believe the situation is stabalizing, and
are obviously hoping for the best.

Players and coaches are very worried right now and essentially
everyone can do nothing but pray for the best. The media is being
quarantined to the media room – as you would expect in these situations
– and there will be no open locker room. Players may be speaking to us
later in the day.

The femoral artery very definitely is in the lower extremities:

The Miami Herald reported that Taylor and other occupants of the
house heard intruders at the rear door and that Taylor was shot in the
leg, but police said they could not confirm those details.

"We’ve yet to determine the circumstances surrounding the shooting," Miami-Dade Police spokeswoman Kathy Webb said.

Miami-Dade police Lt. Nancy Perez, speaking to reporters outside
Taylor’s home, said Taylor "was shot in the lower extremities. He was
airlifted to Ryder Trauma (center at Jackson Memorial Hospital) in
critical condition."

No one can say for certain but as he’s in hospital, with the possibility of transfusions, the outlook is pretty good. No guarantees though, unfortunately.