Backyard Infield

We built at field at our house when my son was 10.  That field got more use than our swimming pool ever did.  One of the best investments we made.  We have a farm and have plenty of room.

Lots of help if you Google about keeping the grass nice.  You'll need to seed, fertilize, water and mow.  As far as construction, best to get a pro to do it.  They can shoot the level and use a bobcat, tractor or other type of dirt mover to level it for you.  The web or your local farm landscaper will be able to help you with the dirt you'll need.  I think we used an agri-lime mixture so it would drain well and wouldn't hold a bunch of water.

You might be best to use a portable mound if you want to be able to switch between 50/70 and 60/90.  I think we built our mound primarily out of clay, and then cut it down and moved it back with the tractor every year when he moved to a new pitching distance.  Bases are easy enough to move when you have the ground anchors installed and use plugs.  We have a four-wheeler and built a drag to pull behind it to maintain the field. 

I know this is just glossing over everything, but I'm sure you'll enjoy it once you have it built.  Most important, unless you're skilled at engineering, have a pretty level piece of ground to begin with or aren't terribly concerned about having it absolutely level, have a pro help you with the basic field construction.

There are diagrams all over the web for proper measurements.  Put a stake at home plate and a stake at the end of your basepath (or wherever you're ending your foul line).  Tie a string between the two and chalk or spray your lines.  You need to do first and third at the same time so you can take continuous measurements all the way down.  Hope that makes sense. 

As far as your mound goes, we made the majority of it with clay.  It makes a nice, firm base. Put some down, and then use a tamper to pack it.  Do it in layers and gradually build it up, packing as you go.

If you use garden soil for your base paths and such, it'll wash out with the first rain.  Better to use agri-lime or something that handles water.  Talk to your local garden center.  They should be able to hook you up.