What do you mean by "That entity isn't the contract"?
Yes, the enforcer is not (necessarily) part of the contract. But if the right incentive system is in place and there is consensus that physical enforcement should happen - anyone approved could take that job/risk and be the enforcer.
With such a system you may not even need a physical enforcer since the risk of not getting the tenant out could be tradeable (like an insurance) and the owner would get his rent even if the tenant cannot be evicted immediately. In case of the tenant, there would be huge negative financial incentives to stay.
This is a spectrum similar to taking out loans and performing liquidations. If the person you are giving a loan too is sketchy you may refuse the loan or charge higher interest.
The same principle applies here as physical eviction is fundamentally about risk. There is an "auction" on the eviction and potential evictors can decide how risky the eviction is. More risky evictions will require a larger payout.
The point is that such a contract requires a central authority that must be capable of evicting the tenant. A "smart contract" which is just some code running on a computer certainly can't do that.
Why do you require a central authority? What you require is this:
1. An incentive to evict someone. Money. Someone needs to get paid to actually do the eviction because they are taking on some risk - physical in this case. It doesn't matter how they get paid. A smart contract can do that.
2. "Social/Legal consensus" that performing the physical eviction is the right thing to do. The person performing the eviction should not get punished for it. If the state and breach of contract is transparent on the blockchain this consensus could be achieved.
3. A way to confirm the eviction to pay the evictor.
Yeah, that should work very well. Say if the third-party (from your description, apparently a band of mercenaries) in charge of enforcing the contract is motivated by economic incentives, what stops any of the parties from providing a stronger economic incentive to the mercenaries so that they don't enforce the contract?
Also, you are ignoring the fact that, at least where I live, only one entity can legally evict a tenant - the county sheriff (in their role as an agent of the court). You cant just hire some random thugs.
Yes, the enforcer is not (necessarily) part of the contract. But if the right incentive system is in place and there is consensus that physical enforcement should happen - anyone approved could take that job/risk and be the enforcer.
With such a system you may not even need a physical enforcer since the risk of not getting the tenant out could be tradeable (like an insurance) and the owner would get his rent even if the tenant cannot be evicted immediately. In case of the tenant, there would be huge negative financial incentives to stay.