The United States has injury worries on the track while the basketball team worries about a familiar foe.

Here are five things to watch at the Olympics on Friday:

1) Men's 4x400 relay: U.S. hopes to continue streak

The United States is lucky to be in the final, lucky, that is, that Manteo Mitchell found a way to finish his opening leg despite a broken fibula. The U.S. will have to find a replacement for him as they challenge the Bahamas for the gold. Also keep an eye on Great Britain, which will have most of the 80,000 fans at Olympic Stadium cheering for them.

Final is at 9:20 p.m. London time (4:20 p.m. ET)

2) Basketball: U.S. dreaming of another final

Team USA faces veteran Argentina in what could be a tough semifinal matchup for the dominant Americans. Sure the U.S. beat them 126-97 in the preliminary round, but it was a one-point game at half and surely the Americans won't score 42 points in the third quarter again. Argentina figures to slow the game down a little and they are expected to have point guard Pablo Prigioni back.

Semifinal game begins at 9 p.m. London time (4 p.m. ET).

3) Cycling: BMX, baby

Eight riders, lots of jumps and bumps, some sharp turns, lots of crashes. As the New York Times said: "Given the carnage on display Thursday, it is safe to assume that whoever designed the BMX racetrack really dislikes BMX racers." Both men and women compete in the event with semifinals and final on Friday.

The first events begins at 3 p.m. London time (10 a.m. ET)

4) Boxing: Superheavyweight super fight

Defending superheavyweight champ Roberto Cammarelle takes on world No. 1 Magomedrasul Medzhidov. Cammarelle, from Italy, is one of only eight boxers to win three medals (he is already guaranteed at least a bronze.) Like his opponent, Medzhidov is on the shorter side for the weight class, but he makes up for a usual reach disadvantage with a powerful punch.

Boxing begins at 1:30 London time (8:30 .m. ET). Superheavyweight matches begin at 10:30 p.m. London time (5:30 p.m. ET)

5) Women's 4x100 meter relay: Chance at redemption

Running with two backups, the U.S. came within a hair of breaking the Olympic record. On Friday, Carmelita Jeter and Allyson Felix will be back in the lineup for the Americans in their matchup against Jamaica. It is unclear if Jeneba Tarmoh, Tianna Madison or Bianca Knight will run again. Each team is looking for redemption as both teams botched handoffs at Beijing.

Round 1 of the relays begins at 8:40 p.m. London time (3:40 p.m. ET)