It's that feeling of being in the zone, completely forgetting about tomorrow's worries. But how does one raise awareness of being in the zone? It is that consciousness that I believe is paramount.
Training your consciousness by playing sports vs sitting in lotus is analogous to training your biceps by rowing vs biceps curls. The latter is more targeted, hence more effective.
When you do what you love and you completely emerge in it, yes, you do get in a state of bliss. But are you conscious of it? If not, which is mostly the case when you see a group of people play soccer in the park, then I don't think that is beneficial in the meditative sense. Your mind is still very much active.
The reason why the traditional way of meditation is so effective (and has therefore been used for millennia), is because it is quite hard to just sit still and do nothing. And really clear your mind of any thought whatsoever.
It is this mental challenge that will really train your consciousness and raise your awareness.
An easier way to get started is to combine the two methods, in the form of tai-chi. Get your exercise, while clearing your mind (and raise your awareness). It has helped me a great deal -- my life has been so much smoother after I trained Tai Chi for 4 intensive months in China.
If you're interested, I blogged about that experience a while back: http://kuomarc.wordpress.com/2012/03/28/tai-chi-in-pursuit-o...