Foster, 48, spent two days in the hospital with head and arm injuries.
The attack happened last week on Foster's usual run on Pulaski Road.
The driver met his accused attacker in court Tuesday.
What was scheduled as a preliminary hearing turned into a court dispute over the attacker's age. Last week, the young man was charged as an adult because prosecutors say he told police he was 18. But on Tuesday the suspect's mother gave the judge birth certificates that proved otherwise.
Foster has 11 staples in his scalp and bandaged hands after he was allegedly beaten with a hammer by a passenger last week. He says it will take a long time to recover form his injuries.
"Right now I have headaches. I can't sleep. Dizzy. My thoughts just get locked until I shake it off," said Foster.
A driver for the past 14 years, Foster was on his routine route on Pulaski Road near 54th Street when a teenage male passenger tried to get on the bus with a dollar student fare. Foster says he asked the young man for a student ID.
"This guy didn't appear to me he looked like a student," said Foster.
Foster says instead of producing an ID, the teenager blindsided him with a punch and an attack with a hammer.
"I was able to put the bus in neutral and brake because I had over 30 people on my bus and not make the situation worse, then I literally jumped out of my seat and we were fighting to hold him down until the police get here," said Foster.
One week after the incident, Foster faced his attacker in court only to be disappointed when a judge transferred the teenager to juvenile court because his mother was able to produce documents showing that the suspect is only 16. Prosecutors claim the young man is 18.
Meantime, several CTA bus drivers came to court to support Foster. Many say violent incidents against CTA drivers are increasing.
"Most bus drivers, we look out for each other. If we see a bus stopped, we are going to stop and see what's going on. That happens a lot, " said Venita Jones, CTA bus driver.
"If we had more security on the buses, undercover security that is, that would help a lot," said Tanya Brown, CTA bus driver.
To protect drivers, the CTA has installed shatter proof driver shields in over 400 of their buses. While the shield program is a pilot, CTA's president says 75 percent of the fleet will have the shields available to them when the installation is complete. The CTA says it is the operator's choice to use the shields. Billy Foster did not have one on his bus.
Foster is on medical leave.