You do not need a full diamond to sharpen fielding skills. A backyard, driveway, or wall can provide plenty of quality reps.
Wall ball: throw a tennis ball or rubber ball against a solid wall and field the rebound. Vary the angle and speed to practice forehand, backhand, and short hops.
Glove work on the knees: kneel facing a partner a few feet away and roll ground balls to each side. This isolates soft hands and proper glove angle without footwork distractions.
Footwork ladder: use chalk or tape to mark a ladder on the ground and practice quick feet, then finish each pass by fielding a rolled ball and making a short throw to a target. Ten minutes a day of these drills builds the habits that show up in games.