Is it possible to get bruised knees and ankles from running a marathon? could it perhaps be that the running tights is too tight?

See details: You tights can't be that tight. Running that distance on asphalt will cause various aches and pains.

Bruises: Not likely from the tights or they would be too uncomfortable to compete in.

Possibly but: Marathons are grueling on the body, and when you finish there can be bruises, pains, etc. Tights normally would not necessarily create the problem, unless they were some type of compression material that was actually cutting off some circulation. Be careful