TCP injection is an attack where the attacker sends crafted packets into an existing TCP session. These packets appear to be part of the session.
The presence of many SYN packets with the same sequence number, source, and destination IP but different payloads indicates that an attacker might be injecting packets into the session.
This method can be used to disrupt communication, inject malicious commands, or manipulate the data being transmitted.
Reference:
Understanding TCP Injection Attacks
Analyzing Packet Captures for Injection Attacks
Network Security Monitoring Techniques