I remember that I got the okay to be on the stationary bike by four weeks; even though I was still mostly on crutches at that point. No real motion restrictions after six weeks. His concern with biking outdoors has to do with the chance of falling, or needing to put your foot out hard to stop a fall. He allows skiing, and most other sports activities at six months, but encourages you to avoid hard impacts until one year. I could see you playing catch at six weeks, or possibly slightly earlier if you were exceedingly careful; just don't dive for the ball, or do any big windups. I know that between four and six weeks, I could have been in serious trouble if I had to really stretch out to catch a ball; not enough stability in the leg yet to support that kind of reach. I think that it is always worth reminding people that after many rebuilding surgeries, like joint or ligament replacements, the body does a lot of remodeling over the first three to four months; basically breaking down bone and soft tissue, and then rebuilding in line with the new parts. Because of this process, many things are actually at there most vulnerable at around the one to four month period, even though we are feeling better every day.