Inwood Park is on the northernmost tip of Manhattan, on the Northeast side of Inwood Hill Park (near Columbia University–Baker Field). The closest subways are the 1-Train (215th Street) and the A-Train (Inwood-207th Street, the final stop). If you're coming from the Upper East Side, the BXM1 express bus drops off right at 207th and Broadway, and can be faster than taking a cross-town bus and tranferring. This is a grass soccer-football field west of the softball fields and adjacent to W. 215 Street and Indian Road. If you're coming here on a weekend, please consult the MTA website for updates on subway and bus schedules.
At the southern end of Riverside Park. Closest subway is the 123-Train (72nd street), and the BC-Trains(72nd street). Walk west from those stations towards the river, go into the park and through a tunnel. Go down the stairs, take a left(go south) and walk along the river. There should be a fenced-off field immediately to your left. Note that for this field, only turf shoes are allowed. You can see examples of acceptable/unacceptable turf shoes here.
Turf field on the Lower East Side, best way to get here is to take the M14D bus. You can also take the L to 1st Ave, the FV to 2nd Ave, or FJMZ to Essex/Delancey Street, but its a bit of a hike. There is an overpass a bit south of E 6th Street that will take you over the FDR and to the field, which is surrounded by a track.