Steve Nash -- All Smiles Outside Court

Steve Nash was in a surprisingly good mood this afternoon on his way into court -- where his ex-wife is currently fighting him tooth and nail to move their kids to L.A. ... and squeeze him for tons of child support.

We asked Steve a bunch of questions on his way back from lunch -- like why he really doesn't want his kids to move to L.A. ... and whether he can elaborate on his refusal to retire from basketball. He responds to one of them. Check the clip.

TMZ broke the story ... Alejandra Nash filed court papers last week, asking a judge to lift a restraining order Steve had obtained against her ... blocking her from moving their 3 kids to L.A.

Alejandra believes Nash wants her to stay put in Phoenix because it's a lot easier to obtain child support in California ... and Steve doesn't want to pay up.

For his part, Steve has said he wants Alejandra to stay in Phoenix in case he's traded or forced to retire ... so the family isn't uprooted a second time.