Softball is a teamsport popular especially in the United States. It is a direct descendant of baseball and the rules of both sports remain substantially similar; baseball is sometimes referred to as hardball to distinguish the two (Wikipedia)
Here, of course, the term "softball" is used metaphorically. In hardball (baseball), the ball travels faster and hurts more when you catch it (or get hit on the head with it). Younger children often play softball for safety reasons, so "hardball" is associated with a faster, somewhat more dangerous game.
A "softball question" is an easy question; a "hardball question" is a difficult question.
Example: At a White House press conference, a reporter asks, "Mr. President, did you enjoy your Easter holiday." That's a softball question.
Another reporter asks, "Mr. President, last year you said you'd have a balanced budget by this year, yet you've cut taxes and increased spending. Can you explain that?" That's a hardball question.
"To play hardball" means to be serious, tough, and competetive; "to play softball" means the opposite.
But as for how to say it in French, with or without preserving the sports connotation, I don't know.
Hope this helps!
P.S. "Hardball" is a political talk show on the MSNBC cable network in the USA, so named because Chris Matthews, the host, asks tough questions....
On parle dans le métier d'un article de complaisance, d'une interview de complaisance... "Une question de complaisance" me semblerait donc convenir, si on souhaite éviter le style familier de "fastoche" et "bateau".