What are the differences between offensive and defensive assists?

When I look at the statistics for various heroes under my Career Profile, I notice that "Offensive Assists" and "Defensive Assists" are listed.

What are offensive and defensive assists, and what are the differences between them?

Solution 1:

Assists in Overwatch are a bit different than assists in other shooters and are largely a support stat. Assists are counted when you contribute in some way to a kill/elimination without dealing damage. Mercy, Lucio, Ana, and Zenyatta (and S:76, I believe) can get defensive assists by providing healing to an attacker while they are dealing damage to a target. Mercy and Zenyatta can get offensive assists by providing damage boosts, either through Mercy's Cadeceus Staff alternate fire or Zenyatta's Orb of Discord. Lucio can get offensive assists with Speed Boost, though he must Amp his songs to get the assists in both cases (Healing Boost for defensive and Speed Boost for offensive).

As Zenyatta is the only hero who can qualify for both assists at the same time, I did some testing and it seems that defensive assists take priority over offensive assists so if an ally with Harmony kills an enemy tagged with Discord, you get a defensive assist rather than an offensive assist.