( CNN ) -- As the swimming meet comes to its final days , the action at track and field begins at the Olympic Stadium . Here 's what to look for as that competition starts and in four other notable sports : . 1 ) Track and field : Sprint queens begin their quests . A few weeks ago , Allyson Felix watched as Jeneba Tarmoh took a celebratory lap at the Olympic Trials , apparently the third qualifier for the Olympics in the women 's 100 meters . But Friday , it 's Felix who will take to the blocks in a quest to finally win a gold medal . There was a second look at the photo finish . The two sprinters had tied , officials ruled . Then the track bosses scrambled to figure out a way to break the tie and decide who would run the event in London . On the day of a scheduled runoff , Tarmoh backed out . She 's still part of the U.S. team , but she 's a member of the relay pool . On Friday , Felix will race twice , seeking a spot in one of Saturday 's semifinals . SI : Life-changing win for Gabby . Track and field begins at 10 a.m. London time ( 5 a.m . ET ) 2 ) Swimming : Speaking of photo finishes . Four years ago , it became one of the most famous photos of the Beijing Games : Shot from the bottom of the pool , Michael Phelps in one lane , Milorad Cavic in the other , two swimmers lunging for Olympic gold . Phelps won the 100-meter butterfly that day by .01 seconds , after catching the Serbian swimmer gliding to the wall as Phelps took a quick , final stroke . Tonight , they will race again . But also look out for Chad le Clos , who beat Phelps in the last few meters of the 200-meter butterfly . Swimming begins at 10 a.m. London time ( 5 a.m . ET ) ; the medley relay heats start at 11:49 a.m. in London ( 6:49 a.m . ET ) followed by four finals in the 7:30 p.m. London time session ( 2:30 p.m . ET ) . 3 ) Tennis : Hopes for happier result at home . Britain 's Andy Murray , who reached Wimbledon finals a few weeks ago , plays Novak Djokovic of Croatia in one men 's singles semifinal . In the other , Roger Federer of Switzerland matches up with Juan Martin del Potro . The women also play singles semifinals ; those matches are Serena Williams of the United States vs. Victoria Azarenka of Belarus , and Russians Maria Sharapova vs. Maria Kirilenko . Photos : American gold medal winners . Both matches begin at noon in London ( 7 a.m . ET ) 4 ) Soccer : A big Hope here , too . The United States is backed by goalie Hope Solo , who gave up two criticized goals early to France and nothing since . The Americans face New Zealand ( nicknamed the Football Ferns ) , which finished third in Group E. In February the Football Ferns nearly beat the United States , but forward Alex Morgan scored two late goals to rally the Americans . They also played a closed door match a few days later ; no results were reported . The highlight match of the day could be Brazil with its great player Marta vs. World Cup champion Japan . Matches start at noon London time ( 7 a.m. ) with the U.S.-New Zealand match at 2:30 p.m. London time ( 9:30 a.m . ET ) 5 ) Judo : Saudi female expected to wear headscarf . At first , judo officials said they would n't allow 16-year-old Wojdan Shaherkani of Saudi Arabia to wear a hijab during her judo match . Shaherkani 's father and Saudi officials insisted she would not compete unless she could wear the headscarf . On Friday , she will be permitted to wear it when she fights Melissa Mojica of Puerto Rico in a round of 32 match . Shaherkani , who is competing at her first major international event , received a special invitation to compete from the International Olympic Committee . Abuse victim wins first U.S. judo gold . Shaherkani is scheduled to fight at 10:33 a.m. London time ( 5:33 a.m . ET ) .
Track and field starts ; women begin quest for 100-meter title . Phelps , Cavic meet again in 100-meter butterfly final . Soccer quarters feature U.S. against the Football Ferns . Saudi woman takes judo mat .