You might remember the battleground radical with this easy mnemonic:
This radical represents a battleground, an ancient battleground in particular. Imagine the legs (儿) of over a hundred samurai pounding the earth (土) as they go slashing ( 丿) away at each other. That would be quite an epic scene.
Using mnemonics to remember Chinese radicals like battleground has a huge impact on how long to learn Mandarin it takes.