A word, when you make anybody fall down with your foot [closed]

I tripped him [up] [with my [outstretched] foot].

From oxforddictionaries.com definition

trip
... 1.1 with object - Cause to stumble and fall.
‘she shot out her foot to trip him up’

You could of course trip someone [up] by throwing a banana skin¹ down in front of them, for example. But most often if unspecified, we assume using my foot.

¹ Arguably not the best example, even though it's perfectly "credible". This use of transitive trip usually implies doing something that blocks or entangles one or both of the victim's feet/legs, rather than lose their footing on an unexpectedly slippery surface.

The word you're looking for is trip. It can be transitive (as in your case) or intransitive.

trip verb

1 no object Catch one's foot on something and stumble or fall.

• ‘he tripped over his cat’
• ‘she tripped up during the penultimate lap’

1.1 with object Cause to stumble and fall.

• ‘she shot out her foot to trip him up’

Oxford

Your sentence would be "I tripped him," although it's usually used with up, as the example shows.