Depends on the league settings and number of teams and such. Also, a fair trade means both managers agreed to it in good faith to improve their teams. Now if you're asking if it's a GOOD trade, I'd lean towards not, all things being equal. Hardy is useful as a power-hitting SS but is pretty one dimensional. Rizzo has a lot of potential and could be a top 20 player someday, but it's no sure thing. Kershaw is either the best pitcher in the game, or in the top 3. So there's no way I'd trade Kershaw in this situation.
When asking for roster advice in these pages, remember there are thousands of different sets of league rules & many different active roster settings. If you want the best replies, be sure to include your leagues particulars in the original post