I have a 2009 Polaris 800 Touring ATV. The engine starts good,but going down the trail and stopping The 20 amp fuse for the ignition blows.

SOURCE: 20-amp starter/ignition fuse keeps blowing & car won't start

its the starter

SOURCE: 30 amp ignition fuse in engine compartment blows at start

It sounds like a bad ignition switch or something is grounding out.Try to isolate the problem to key positions.See if the fuse blows when you turn the key to ACC(when your dash lights come on without starting)If the fuse does not blow then when you go to start it and it blows it could be one of many problems,the more common ones could be ignition switch,wiring,starter relay,starter soleniod,or perhaps the starter itself is shorting out,this can sometimes happen when a starter goes bad.

SOURCE: ignition switch fuse terminal is blowing red 40 amp fuse when i try to replace it

A fuse that is consistently blowing is telling you that there is a short in that system. Don't attempt to bridge it or use a larger amp fuse or you will have a major problem. You will need to start tracing wiring to destinations to find the short. If while moving harnesses around problem ceases to exist, look at nearby items where you are working and try to locate what was grounding. Sometimes people will stop if short disappears, leaving open the possibility of it happening again.
If you are not comfortable working with wiring, then leave it to professionals who do this every day. It's not really difficult but requires patience and a good bit of knowledge to do this right!

SOURCE: 20 amp ignition fuse keeps blowing

I'm curious, does this vehicle have an alarm/remote starter? If so I expect the installer didn't wire it correctly ... it was an all too frequent issue, with inexperienced installers we had .... I would first suspect any add-on device first (if any) ... In answer to your question ... I know it does have a relay (Starter solenoid is a relay and built onto the starter) As far as it being a relay or the IGN switch ... I'm skeptical.

SOURCE: Wiper fuse keeps blowing intermittently.

It looks like the wire circuit for the wiper motor is touching the car body when shaken so the only thing you can do is shake the wires and terminals yourself while engine is running then maybe you can pinpoint where the earthing is.