Fair points, and those are the concerns. But if it works, he's worth 5 WAR every year. If it only kinda works, he's still probably going to be worth 2.5 (Randy Wells 09-10 range). If you don't think he can even replicate Wells, then sure, leave him alone. I'm less worried about him replicating Wells than I am with him ending up broken given his history. It could work, but even if he gives you 150 IP and then gets hurt, WAR may say you gained something, but you've lost a valuable guy by taking an unnecessary risk. Of course this assumes that starting puts Marshall at greater risk for injury than relieving, which is probably not a valid thing to assume. I think it was John Smoltz that said closing put much more wear-and-tear on his arm than starting. One of Marshall's recurring problems was with blisters, which would definitely be at a higher risk of recurring if he's starting. Maybe Marshall ends up a 5 WAR guy, but I don't think that's so likely that it's worth the injury and performance risk. The odds of SP Marshall + [whoever replaces his pen innings] exceeding the value of [Wells/Cashner/whoever he would be replacing] + RP Marshall are very slim. Ideally, Marshall would be "replacing" CJ Wilson, and saving the Cubs $100M or whatever that they can then spend elsewhere. That's best-case, of course. And I know the money is extremely loose and doesn't account for Marshall's salary. Point is SM is dramatically cheaper. Offer him a 4/$15M extension and tell him you'd like to try him as a starter. He'd be an enormous value and a huge asset at those prices, if he can stick.